FORD DIGITAL

CODE READER
(Front Cover)
Table of Contents
Title Page No.

YOU CAN DO IT! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

CHAPTER 1 - GENERAL INFORMATION

SAFETY PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
HOW TO USE THIS MANUAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
VEHICLE SERVICE MANUALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
VEHICLES COVERED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
PRELIMINARY VEHICLE DIAGNOSIS WORKSHEET . . . . . . . . . . . . . . . . . 8

CHAPTER 2 - ABOUT DIAGNOSTIC SYSTEMS

WHAT ARE THE ADVANTAGES OF USING COMPUTER CONTROL
SYSTEMS ON VEHICLES? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
HOW DOES A COMPUTER SYSTEM WORK ON A VEHICLE, AND
WHAT IS IT’S MAIN PURPOSE? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
HISTORY OF FORDS ELECTRONIC ENGINE CONTROL (EEC)
SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
FORD COMPUTER SYSTEM OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

CHAPTER 3 - ABOUT THE FORD CODE READER

BEFORE YOU BEGIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
TEST CONNECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
CONNECTING THE FORD CODE READER TO THE VEHICLE’S
TEST CONNECTOR(S) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
FUNCTIONS OF THE FORD CODE READER . . . . . . . . . . . . . . . . . . . . . . . . . . 19

CHAPTER 4 - RETRIEVING CODES

OVERVIEW OF FAULT CODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
OVERVIEW OF FORD CODE RETRIEVAL PROCESS . . . . . . . . . . . . . . . . . 24
KEY ON ENGINE OFF (KOEO) TEST PROCEDURES
(EEC-IV SYSTEMS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
ENGINE TIMING CHECK (EEC-IV SYSTEMS) . . . . . . . . . . . . . . . . . . . . . . . 30
KEY ON ENGINE RUNNING (KOER) SELF TEST (EEC-IV SYSTEMS) . . . . 32
ERASING CODES FROM EEC-IV SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . 37
ADDITIONAL TESTS FOR EEC-IV SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . 38
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS CAR AND
TRUCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
RETRIEVING FAULT CODES FROM MCU SYSTEMS . . . . . . . . . . . . . . . . . 65
KEY ON ENGINE OFF (KOEO) SELF TEST (MCU SYSTEMS) . . . . . . . . . . 66
KEY ON ENGINE RUNNING (KOER) SELF TEST (MCU SYSTEMS) . . . . . 68
FAULT CODE DEFINITIONS FOR MCU SYSTEMS CAR AND TRUCK . . . . 71

CHAPTER 5 - TROUBLESHOOTING
CODE READER TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . 75

CHAPTER 6 - GLOSSARY
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
GLOSSARY OF TERMS AND ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . 77

CHAPTER 7 - WARRANTY AND SERVICE

LIMITED ONE YEAR WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
SERVICE PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

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Read Fault Codes
• Ensure ignition is off.

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• Turn on ignition. DO
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Pinpoint Problem Areas

test

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• Locate fault code(s) in the

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Press TEST/HOLD button
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General Information
SAFETY PRECAUTIONS 1
SAFETY PRECAUTIONS
To avoid personal injury, instrument damage and/or
damage to equipment under test; do not operate the
Ford Digital Code Reader before reading this manual.
This manual describes common test procedures used by
experienced service personnel and technicians. Many test
procedures require precautions to avoid accidents that can
result in personal injury, and/or vehicle or equipment damage.
Always read your vehicle’s service manual and follow its safety
precautions before any test or service procedure is performed.
a. When an engine is running, it produces carbon monoxide
(a toxic and poisonous gas). To prevent serious injury or
death from carbon monoxide poisoning, operate a vehicle
ONLY in a well-ventilated area.
b. To protect your eyes from propelled objects as well as hot
or caustic liquids, always wear approved safety eye
protection.
c. When an engine is running, several objects rotate at a
very high rate of speed (cooling fan, pulleys, fan belt etc.).
To avoid serious injury, always be conscious of moving
parts, and keep a safe distance from all these items as
well as other potentially moving objects.
d. Engine parts become extremely hot when the engine is
running. To prevent severe burns, avoid contact with hot
engine parts.
e. Before starting an engine for troubleshooting, make sure
the parking brake is engaged. Put the transmission in
“park” (for automatic transmission) or “neutral” (for
manual transmission). Block the drive wheels with a
suitable blocking device.
f. Connecting or disconnecting test equipment when the
ignition is “on” can cause a spark. This spark is
potentially damaging to the test equipment and to the
vehicle’s electronic components. Always turn the ignition
“off” before connecting or disconnecting any test
equipment.
g. To prevent damage to the on-board computer when taking
vehicle electrical measurements, always use a digital
multimeter with at least 10 Megohms of impedance.

1 Chapter 1
 General Information
1 HOW TO USE THIS MANUAL

h. The vehicle’s battery produces highly flammable hydrogen

gas. To prevent an explosion, keep all sparks, high
temperature items or open flames away from the battery.
i. Don't wear loose clothing or jewelry when working on an
engine. Loose clothing can get caught on the fan, pulleys,
belts, etc. Jewelry is highly conductive, and can cause a
severe burn if it makes contact between a power source
and ground.

INTRODUCTION
Congratulations, you have purchased one of the most
technologically advanced Code Readers on the market today.
The Ford Digital Code Reader uses sophisticated electronics
designed to retrieve engine and transmission (applicable Ford
vehicles only) Diagnostic Trouble Codes (DTC's) from the
vehicle's computer.

HOW TO USE THIS MANUAL

This Code Reader and manual are designed for use both by
consumers with little or no experience in retrieving codes, or by
experienced technicians desiring a more in-depth explanation
of Ford Computer Command Control system basics.
If you are having problems with your vehicle and only want to
know if any Diagnostic Trouble Codes are present in the vehicle’s
computer system, read the “Safety Precautions” (page 1) and
“Vehicles Covered” (page 4), then proceed to Chapter 3 and follow
the simple directions to retrieve the codes. The codes retrieved,
and their definitions, will give you valuable information and a
starting point from which to proceed to the next step.
Once the codes have been retrieved, you can choose to:
• Take your vehicle to an Automotive Service Center
for repair: Take your vehicle, a copy of the completed
Preliminary Vehicle Diagnosis Worksheet (see pages 8 - 10)
and codes retrieved to your technician for evaluation. This
will demonstrate to your technician that you are an
informed motorist and will also assist him in pinpointing
the location of the problem.

Chapter 1 2
General Information
VEHICLE SERVICE MANUALS 1
• Attempt to fix the problem yourself: If you choose to
fix the problem yourself, read and follow all of the
manual’s recommendations and procedures. Additional
tools, text equipment (multimeter, timing light, etc.) and a
vehicle repair manual containing Ford’s Diagnostic Trouble
Code Service Procedures for your vehicle will be needed.

VEHICLE SERVICE MANUALS

It is recommended that you consult the manufacturer’s service
manual for your vehicle before any test or repair procedures
are performed.
Contact your local car dealership, auto parts store or bookstore
for availability of these manuals. The following companies
publish valuable repair manuals:
■ Haynes Publications
861 Lawrence Drive, Newbury Park, California 91320
Phone: 800-442-9637
■ Mitchell International
14145 Danielson Street, Poway, California 92064
Phone: 888-724-6742
■ Motor Publications
5600 Crooks Road, Suite 200, Troy, Michigan 48098
Phone: 800-426-6867
FACTORY SOURCES
Ford, GM, Chrysler, Honda, Isuzu
Hyundai and Subaru Service Manuals
■ Helm Inc.
14310 Hamilton Avenue, Highland Park, Michigan 48203
Phone: 800-782-4356

3 Chapter 1
 General Information
1 VEHICLES COVERED - CARS

VEHICLES COVERED
CAR - Ford, Lincoln, Mercury Computer System/Code Reader
Application Table
The following table is applicable to all models (excluding
Diesel) of Ford, Lincoln and Mercury vehicles.
Fuel Systems
8th VIN (Carburetor Computer
Engine Digit** Model) Application/Special Notes System
1981-1982
2.3L I-4 OHC A FBC Capri, Cougar, Fairmont, MCU
(6500-2V)* Granada, Mustang, Zephyr
3.8L V-6 3 FBC Continental, Cougar, Granada,
(7200 VV-2V)* T-Bird (Cal. only)
4.2L V-8 D Capri, Cougar, Fairmont,
Granada, Mark VII, Mustang,
T-Bird, Zephyr
5.0L V-8 F Capri, Continental (Cal. only),
Granada, Mark VII, Mustang
5.8L V-8 G All Federal Police models
1983
2.3L I-4 OHC A FBC Capri, Fairmont, LTD, Marquis, MCU
(6500-2V)* Mustang
3.8L V-6 3 FBC Continental, Cougar, Granada,
(7200-VV-2V)* T-Bird (Cal. only)
5.0L V-8 F Capri, Continental, Cougar,
Fairmont, Granada, Mark VII,
5.8L V-8 G Mustang, T-Bird, Zephyr
1.6L I-4 5, 2 EFI, EFI Turbo Escort, EXP, LN7, Lynx EEC-IV
2.3L I-4 5 EFI Turbo Capri, Cougar, Mustang, T-Bird
2.3L I-4 HSC R, J FBC (6149)* Capri, Fairmont, LTD, Marquis,
Mustang, Tempo, Topaz, Zephyr
1984-1986
5.8L V-8 G FBC Crown Victoria, Grand Marquis MCU
(7200-VV-2V)*
1.6L I-4 4, 5 EFI Escort, EXP, Lynx EEC-IV
8 EFI Turbo
2.3L I-4 A, J, R FBC Capri, Cougar, LTD, Marquis,
2.3L I-4 OHC (YFA)* (6149)* Mustang, Tempo, Topaz
2.3L I-4 T, W EFI Turbo Capri, Cougar, Merkur XR4Ti,
Mustang, T-Bird
2.3L I-4 HSC S, X CFI Tempo, Topaz
3.8L V-6 3 CFI Capri, Cougar, LTD, Marquis,
Mustang, T-Bird
5.0L V-8 F, M CFI, SEFI Capri, Continental, Colony Park,
Cougar, Country Squire, Crown
Victoria, Grand Marquis, LTD,
Mark VII, Marquis, Mustang,
T-Bird, Town Car

Chapter 1 4
General Information
VEHICLES COVERED - CARS 1
Fuel Systems
8th VIN (Carburetor Computer
Engine Digit** Model) Application/Special Notes System
1987-1993
5.8L V-8 G FBC 1987-91 Police vehicles only MCU
(7200 VV-2V)* (carbureted)
1.9L I-4 J, 9 EFI, CFI, SFI Escort, EXP, Lynx, Tracer EEC-IV
2.0L I-4 A SEFI Probe (1993 manual transmis-
sion only)
2.3L I-4 A FBC (YFA)* Capri, LTD, Marquis, Mustang
(1996 models)
2.3L I-4 OHC A, M EFI Mustang
2.3L I-4 T, W EFI Turbo Capri, Cougar, Merkur,
Mustang, T-Bird, XR4Ti
2.3L I-4 HSC S, X CFI, EFI, SEFI Tempo, Topaz
2.5L I-4 D EFI, CFI Sable, Taurus
3.0L V-6 1, U, Y EFI, SEFI, SFI Probe, Sable, Taurus, Tempo,
3.0L V-6 SHO Topaz (VIN 1 Taurus models are
Flexible Fuel)
3.8L V-6 3, 4, C, R CFI, EFI, SFI Capri, Continental, Cougar,
LTD, Marquis, Mustang, Sable,
T-Bird,Taurus
4.6L V-8 W, V SEFI Crown Victoria, Grand Marquis,
Mark VII, Town Car
5.0L V-8 F, M, E, SEFI Capri, Continental, Cougar,
T, D, 4 Crown Victoria, Grand Marquis,
Mark VII, Mustang, Mustang
Cobra, T-Bird, Town Car
1994
1.9L I-4 J SFI Escort, Topaz, Tracer EEC-IV
2.0L I-4 A SFI Probe
3.0L V-6 1, U, Y SFI Sable, Taurus, Tempo (VIN 1
Taurus models are Flexible Fuel)
3.8L V-6 4 SFI Continental, Cougar, Sable,
3.8L V-6 SC R Taurus, T-Bird
4.6L V-8 W, V SFI Crown Victoria, Grand Marquis,
Mark VIII, Town Car
5.0L V-8 T, D SFI Mustang, Mustang Cobra
1995
1.9L I-4 J SFI Escort, Tracer EEC-IV
2.0L I-4 A, 3 SFI Contour, Mystique, Probe
2.5L V-6 L SFI Contour, Mystique
3.0L V-6 1, U SFI Sable, Taurus (VIN 1 Taurus
3.0L V-6 SHO Y models are Flexible Fuel)
3.8L V-6 4 SFI Cougar, Sable, Taurus, T-Bird
3.8L V-6 SC R
4.6L V8 DOHC V SFI Mark VIII
5.0L V-8 HO T SFI Mustang
5.0L V-8 SHP D

5 Chapter 1
 General Information
1 VEHICLES COVERED - TRUCKS/VANS

NOTES
* Carburetor Model. Carburetor model numbers are usually stamped on top of the
carburetor, or on a metal tab attached to the carburetor. Consult your vehicle’s repair
manual for proper identification.
**VIN Number. The VIN number(s) used in this column identify the vehicle’s engine
type. This number is the 8th digit of the VIN (Vehicle Identification Number). Consult
your vehicle’s repair manual for details.
Application Table Definitions. CFI = Central Fuel Injection; DOHC = Dual
Overhead Cam; EFI = Electronic Fuel Injection; FBC = Feedback Carburetor; HSC =
High Swirl Combustion; MFI = Multiport Fuel Injection; OHC = Overhead Cam; SC =
Super Charged; SEFI = Sequential Electronic Fuel Injection; SFI = Sequential Fuel
Injection; SHO = Super High Output

TRUCKS/VANS - Ford Computer System Code Reader

Application Table
The following table is applicable to all models of Trucks, Vans
and Utility Vehicles.

Fuel Systems
8th VIN (Carburetor Computer
Engine Digit** Model) Application/Special Notes System
1981-1982
4.9L I-6 E FBC (YFA)* Bronco (Cal. only); E and F MCU
Series Trucks/Vans
1983
2.0L I-4 C FBC (2150A)* Ranger Pickup MCU
2.3L I-4 OHC A FBC (YFA)* Ranger Pickup (excluding high
altitude)
4.9L I-6 E FBC (YFA)* Bronco (Cal. only), E and F
Series Trucks/Vans (8500 lb.
GVW or less only)
2.8L V-6 S FBC (2150A)* Bronco II and Ranger Pickup EEC-IV
1984
2.0L I-4 C FBC (YFA)* Ranger Pickup MCU
2.3L I-4 OHC A FBC (YFA)*
2.8L V-6 S FBC (2150A)* Bronco II, Ranger Pickup EEC-IV
4.9L I-6 Y FBC (YFA)* Bronco, E and F Series Trucks/
5.0L V-8 F FBC (2150A)* Vans (8500 lb. GVW or less only)
5.8L V-8 G FBC (2150A)*
1985-1990
2.3L I-4 OHC A EFI Aerostar, Bronco II, Ranger EEC-IV
2.9L V-6 T EFI (excluding Diesel)
2.8L V-6 S FBC (2150A)* Bronco, E and F Series Trucks/
4.9L I-6 Y, 9 FBC (YFA)*, Vans (8500 lb. GVW or less only)
EFI
5.0L V-8 F FBC (2150A)*
5.0L V-8 N EFI

Chapter 1 6
General Information
VEHICLES COVERED - TRUCKS/VANS 1
Fuel Systems
8th VIN (Carburetor Computer
Engine Digit** Model) Application/Special Notes System
1985-1990 (Cont)
5.8L V-8 G FBC (2150A)* E and F Series Trucks/Vans EEC-IV
7.3L V-8 M Diesel (8500 lb. GVW or less only)
7.5L V-8 G EFI
1991-1994
2.3L I-4 OHC A EFI, MFI Ranger EEC-IV
2.9L V-6 T EFI
3.0L V-6 U EFI, SEFI, SFI Aerostar, Ranger
4.0L V-6 X EFI, MFI Aerostar, Explorer, Ranger
4.9L I-6 Y, H EFI, MFI, SFI Bronco, E and F Series Trucks/
5.0L V-8 N EFI, MFI, SFI Vans (8500 lb. GVW or less only)
5.8L V-8 H, R EFI, MFI, SFI
7.3L V-8 M Diesel E and F Series Trucks/Vans
7.3L V-8 K Turbo Diesel (Excludes 1994 diesel models)
7.5L V-8 G EFI, MFI
1995
3.0L V-6 U SFI Aerostar (Excludes Explorer, EEC-IV
Ranger and Windstar)
4.0L V-6 X SFI
4.9L I-6 Y SFI E and F series Trucks and Vans
(Excludes Natural Gas equipped
vehicles)
5.0L V-8 N SFI Bronco, E and F series Trucks
and Vans
5.8L V-8 H, R MFI
7.5L V-8 G MFI E-350; F-250-350 (Excludes
California ); F-Super Duty
(Excludes Diesel)
NOTES
* Carburetor Model. Carburetor model numbers are usually stamped on top of the
carbure-tor, or on a metal tab attached to the carburetor. Consult your vehicle’s repair
manual for proper identification.
**VIN Number. The VIN number(s) used in this column identify the vehicle’s engine
type. This number is the 8th digit of the VIN (Vehicle Identification Number). Consult
your vehicle’s repair manual for details.
Application Table Definitions. EFI = Electronic Fuel Injection; FBC = Feedback
Carburetor; MFI = Multiport Fuel Injection; OHC = Overhead Cam; SC = Super
Charged; SEFI = Sequential Electronic Fuel Injection; SFI = Sequential Fuel Injection

7 Chapter 1
 General Information
1 PRELIMINARY VEHICLE DIAGNOSIS WORKSHEET

PRELIMINARY VEHICLE DIAGNOSIS WORKSHEET

The purpose of this form is to help you gather preliminary information
on your vehicle before you retrieve codes. By having a complete
account of your vehicle's current problem(s), you will be able to
systematically pinpoint the problem(s) by comparing your answers to
the fault codes you retrieve. You can also provide this information to
your mechanic to assist in diagnosis and help avoid costly and
unnecessary repairs. It is important for you to complete this form to help
you and/or your mechanic have a clear understanding of your vehicle's
problems.

NAME:
DATE:
VIN*:
YEAR:
MAKE:
MODEL:
ENGINE SIZE:
VEHICLE MILEAGE:
*VIN: Vehicle Identification Number, found at the base of the
windshield on a metallic plate, or at the driver door latch area (consult
your vehicle owner's manual for location).
TRANSMISSION:
❑ Automatic
❑ Manual

Please check all applicable items in each category.

DESCRIBE THE PROBLEM:

Chapter 1 8
General Information
PRELIMINARY VEHICLE DIAGNOSIS WORKSHEET 1
WHEN DID YOU FIRST NOTICE THE PROBLEM:
❑ Just Started
❑ Started Last Week
❑ Started Last Month
❑ Other:

LIST ANY REPAIRS DONE IN THE PAST SIX MONTHS:

PROBLEMS STARTING
❑ No symptoms ❑ Cranks, but will not start
❑ Will not crank ❑ Starts, but takes a long time

ENGINE QUITS OR STALLS

❑ No symptoms ❑ Right after vehicle comes to a stop
❑ Right after starting ❑ While idling
❑ When shifting into gear ❑ During acceleration
❑ During steady-speed driving ❑ When parking

IDLING CONDITIONS
❑ No symptoms ❑ Is sometimes too fast or too slow
❑ Is too slow at all times ❑ Is rough or uneven
❑ Is too fast ❑ Fluctuates up and down

RUNNING CONDITIONS
❑ No symptoms ❑ Backfires
❑ Runs rough ❑ Misfires or cuts out
❑ Lacks power ❑ Engine knocks, pings or rattles
❑ Bucks and jerks ❑ Surges
❑ Poor fuel economy ❑ Dieseling or run-on
❑ Hesitates or stumbles on
accelerations

9 Chapter 1
 General Information
1 PRELIMINARY VEHICLE DIAGNOSIS WORKSHEET

AUTOMATIC TRANSMISSION PROBLEMS (if applicable)

❑ No symptoms ❑ Vehicle does not move when in
❑ Shifts too early or too late gear
❑ Changes gear incorrectly ❑ Jerks or bucks

PROBLEM OCCURS
❑ Morning ❑ Afternoon ❑ Anytime

ENGINE TEMPERATURE WHEN PROBLEM OCCURS

❑ Cold ❑ Warm ❑ Hot

DRIVING CONDITIONS WHEN PROBLEM OCCURS

❑ Short - less than 2 miles ❑ With headlights on
❑ 2 ~ 10 miles ❑ During acceleration
❑ Long - more than 10 miles ❑ Mostly driving downhill
❑ Stop and go ❑ Mostly driving uphill
❑ While turning ❑ Mostly driving level
❑ While braking ❑ Mostly driving curvy roads
❑ At gear engagement ❑ Mostly driving rough roads
❑ With A/C operating

DRIVING HABITS
❑ Mostly city driving ❑ Drive less than 10 miles per day
❑ Highway ❑ Drive 10 to 50 miles per day
❑ Park vehicle inside ❑ Drive more than 50 miles per day
❑ Park vehicle outside

GASOLINE USED
❑ 87 Octane ❑ 91 Octane
❑ 89 Octane ❑ More than 91 Octane

WEATHER CONDITIONS WHEN PROBLEM OCCURS

❑ 32 ~ 55° F (0 ~ 13° C) ❑ Above 55° F (13° C)
❑ Below freezing (32° F / 0° C)

CHECK ENGINE LIGHT / DASH WARNING LIGHT

❑ Sometimes ON ❑ Always ON ❑ Never ON
PECULIAR SMELLS
❑ "Hot" ❑ Gasoline
❑ Sulfur ("rotten egg") ❑ Burning oil
❑ Burning rubber ❑ Electrical

STRANGE NOISES
❑ Rattle ❑ Squeak
❑ Knock ❑ Other

Chapter 1 10
About Diagnostic Systems
WHAT ARE THE ADVANTAGES OF COMPUTER CONTROL SYSTEMS? 2
WHAT ARE THE ADVANTAGES OF USING COMPUTER
CONTROL SYSTEMS ON VEHICLES?
Vehicle Computer Control Systems can perform millions of
calculations in one second, making them an ideal substitution
for the much slower mechanical engine controls. By switching
from mechanical engine controls to electronic engine controls,
vehicle manufacturers were able to control fuel delivery and
spark timing as well as other engine functions (some newer
Computer Control Systems also control transmission, brakes,
charging, body and suspension systems) more precisely. This
made it possible for vehicle manufacturers to comply with the
new, tougher emission and fuel efficiency standards mandated
by State and Federal Governments.

HOW DOES A COMPUTER SYSTEM WORK ON A

VEHICLE, AND WHAT IS IT’S MAIN PURPOSE?
The main purpose of the vehicle’s Computer Control System is
to provide maximum engine performance with the least
amount of air pollution and the best fuel efficiency possible.
The Computer Control System consists of the on-board
computer, and several related control devices (sensors,
switches, and actuators). Most on-board computers are located
inside the vehicle behind the dashboard, under the passenger’s
or driver’s seat, or behind the right kick panel. Some
manufacturers may still position it in the engine compartment.
The sensors, switches, and actuators are devices such as
oxygen sensors, coolant temperature sensors, throttle position
sensors, fuel injectors, etc., that are located throughout the
engine, and are connected by electrical wiring to the on-board
computer.
The on-board computer is the heart of the Computer Control
System. The computer contains several programs with pre-
programmed reference values for air/fuel ratio, spark or
ignition timing, injector pulse width (how much fuel is injected
into the engine), engine speed, etc., for all possible driving
conditions (idle, low speed driving, high-speed driving, low
load, high load, etc.). The pre-programmed reference values
represent the ideal air/fuel mixture, spark timing,
transmission gear selection, etc., for any driving condition.
These values are programmed at the factory and are specific to
each vehicle model.

11 Chapter 2
 About Diagnostic Systems
2 HOW DOES A COMPUTER SYSTEM WORK ON A VEHICLE?

The on-board computer receives information (inputs) from

sensors and switches located throughout the engine. These
devices monitor critical engine conditions (coolant
temperature, engine speed, engine load, throttle position,
air/fuel ratio etc.). The computer compares the actual values
received from these sensors with the reference values that are
programmed in it’s memory, and makes corrections as needed
so that the sensor values always match the pre-programmed
reference values for that particular driving condition.
Since vehicle operating conditions are constantly changing, the
computer continuously makes adjustments or corrections
(especially to the air/fuel mixture and spark timing) to keep all
the engine systems operating within the pre-programmed
reference values.
NOTE: The computer does not make the adjustments or
corrections directly. It commands other devices such as the fuel
injectors, idle air control, EGR valve or Ignition Module to
perform these functions. These devices are called Actuators
because they initiate an action in response to the commands of
the computer.

How a Special Program in the Computer Detects and

Reports Problems in the System
• Beginning in 1988 California’s Air Resources Board (CARB),
and later, the Federal Government's Environmental
Protection Agency (EPA), required vehicle manufacturers
to include a self diagnostic program capable of identifying
an emissions-related fault in a system in their On-board
Computers. The first generation of On-board
Diagnostics came to be known as OBD I.
NOTE: Most manufacturers (including Ford) began
installing computers with On-Board Diagnostics on some
of their vehicles as early as 1981.
• OBD I is a set of self-testing or self-diagnosing instructions
that are programmed into the vehicle’s on-board computer.
• The program is specifically designed to detect failures in
the sensors, actuators, switches and wiring of the various
vehicle emissions-related systems (fuel injection system,
ignition system, EGR system, catalytic converter, etc.). If
the computer detects a failure in any one of these
components or systems, it alerts the driver by
illuminating a light on the dash (the light will illuminate
only if it is an emissions-related problem).

Chapter 2 12
About Diagnostic Systems
HISTORY OF FORD’S EEC SYSTEMS 2
• The computer also assigns a numeric code (OBD I systems
utilized a 2 or 3 digit code) for each specific problem that it
detects, and stores these codes in it’s memory for later
retrieval. The codes can be retrieved from the computer’s
memory with the use of a device called a “Code Reader” or
a “Scan Tool”.

• In addition to storing Diagnostic Trouble Codes for

detected problems, most Ford computer systems are also
designed to perform special Self Tests in real time, and to
send the test results to the Code Reader as two- or three-
digit Diagnostic Trouble Codes.
NOTE: With the exception of some 1994 and 1995 vehicles most
vehicles from about 1982 to 1995 are equipped with OBD I
systems.

HISTORY OF FORD’S ELECTRONIC ENGINE CONTROL

(EEC) SYSTEMS
1978: Ford Motor Company introduces its first “Electronic
Engine Control (EEC-I)” system. This system was very
limited in the control of engine functions and only controlled
ignition timing, EGR flow and the air pump's injection of air
into the exhaust.
1979: Ford introduces the EEC-II system. This system added
air/fuel ratio control (feedback carburetor), throttle kicker
(controls engine idle speed during start up and AC function)
and canister purge control to the ECC-I system.
1980: Ford introduces the EEC-III system. This system
included all the sensors used by the ECC-II system, with the
addition of a temperature Sensor. In 1981, the ECC-III system
was modified to include controls for the new Electronic Fuel
Injection systems. The EEC-III system was used on some
models of Ford vehicles until 1984.
1980: In addition to the EEC-III system, Ford introduced
another computer control system, called the “Microprocessor
Control Unit (MCU)”. This system was used on a limited
number of Ford vehicles up until 1991.
1983: Ford introduces the “Electronic Engine Control - IV
(EEC-IV)” system. This system is capable of controlling a
larger number of sensors, switches and actuators, and was
used on a greater number of Ford vehicles. The ECC-IV
system was used from 1983 to 1995.

13 Chapter 2
 About Diagnostic Systems
2 FORD COMPUTER SYSTEM OVERVIEW

1994: Ford introduces the EEC-V system (OBD-II). This is a

highly sophisticated system that uses more special programs
to enhance the computer's capability to monitor, detect and
report failures, especially to the vehicle's emission system.
This system was introduced on a limited number of 1994 and
1995 vehicles. Starting in 1996, all Ford vehicles (cars and
light trucks) sold in the US are equipped with the EEC-V
system.
NOTE: The Ford Digital Code Reader is compatible only with
the MCU and the EEC-IV Computer Control systems. The
EEC-I, EEC-II, EEC-III and the EEC-V (OBD-II) systems
require specialized equipment to diagnose computer problems
and/or retrieve fault codes and are not compatible with the
Ford Digital Code Reader.

FORD COMPUTER SYSTEM OVERVIEW

Ford vehicle's computers are factory-programmed with special
Self-Testing instructions that are specially designed to detect
any failures in the various systems that the vehicle's computer
monitors and controls. The computer monitors the vehicle’s
sensors (oxygen sensors, coolant temperature sensors, mass
airflow sensors, EGR valve, MAP sensors, etc.) and actuators
(fuel injectors, EGR system, idle air control, cooling fan, canister
purge solenoid, spark advance, etc.) for proper operation. All of
these devices are connected to the vehicle's computer by wires.
The sensors communicate with the computer by sending
voltage signals (inputs) that correspond with the vehicle's
current operating condition. If the voltage that the computer
receives from a particular sensor does not agree with the
voltage value that is programmed in its memory for that
particular driving condition. A Diagnostic Trouble Code is
generated that pertains to that particular circuit or system.
Actuators receive commands from the computer in the form of
voltage signals to perform a certain functions or adjustment.
Example: The computer might command a fuel injector to
increase the amount of fuel injected into the engine. After
the computer commands the fuel injector to inject more fuel
in to the engine, it then monitors the voltage signal from
that injector to ensure that the injector has responded. If
the fuel injector's voltage signal does not change, it
indicates that the fuel injector is not responding to the
computer’s command. The computer then determines that
there is a problem in the injector or injector circuit, and
generates a code related that particular problem. This code
is sent to the Code Reader during the Self Test procedure.

Chapter 2 14
About Diagnostic Systems
FORD COMPUTER SYSTEM OVERVIEW 2
IMPORTANT: When the computer is in Self Test mode (is
testing the sensors or actuators for proper operation), it relies
on voltage signals that it sends to and/or receives from the
sensors or actuators to determine whether or not these
components are operating properly. The sensors and actuators
are all connected to the computer by wires. If any defects are
present in any part of the circuit that connects these devices to
the computer (such as defective connectors or wires, faulty
grounds, improper voltage, shorts etc.), the voltage signal that
the computer receives from these devices will be affected. The
computer has no way of determining if the improper voltage
signal is being caused by a defect in the circuit or by the sensors
or actuators themselves. Keep this in mind when servicing
Fault Codes, and do not replace any devices (sensors or
actuators) before checking the complete circuit (or circuits) that
are part of the device from which the code was generated.

15 Chapter 2
 About Diagnostic Systems
2

Chapter 2 16
About the Ford Code Reader
BEFORE YOU BEGIN 3
BEFORE YOU BEGIN

• Fix any known mechanical problems before performing

any test.
Make a thorough check before starting any test procedure.
Loose or damaged hoses, wiring or electrical connectors are
often responsible for poor engine performance, and in some
cases they may cause a "false" fault code.
Please read your vehicle's service manual for proper
connection of vacuum hoses, electrical wiring and wiring
harness connectors. Check the following areas:
a. All fluid levels - check the oil, power steering, trans-
mission (if applicable), coolant and other engine fluids.
b. Air cleaner and ducts - check for holes, rips, excessive
dirt in filter, and for disconnected ducts. You may wish to
check your owner's manual to determine when you should
change the air filter.
c. Belts - check for ripped, torn, brittle, loose or missing belts.
d. Mechanical linkage associated with sensors - Refer
to your vehicle's service manual for locations.
e. Rubber (vacuum/fuel) and steel hoses - check for leaks,
cracks, blockage or other damage; check for proper routing.
f. Spark plugs and wires - check for damaged, loose,
disconnected or missing spark plug wires.
g. Battery terminals - make sure battery terminals are
clean and tight; check for corrosion or broken connections.
Verify proper battery and charging system voltage.
h. Electrical connectors and wiring - make sure wire
insulation is in good condition and there are no exposed
wires. Make sure all cables are connected securely.
i. Verify that the engine is mechanically sound. If necessary,
perform a compression check, engine vacuum check,
timing check (if applicable), etc.

Preparing The Code Reader For Use

Installing the Battery
■ 2 - "AA" batteries are required to perform tests.
■ Batteries sold separately.
a. Remove the battery compartment cover from the back of
the Code Reader.

17 Chapter 3
 About the Ford Code Reader
3 TEST CONNECTORS

b. Match battery terminals with battery connector contacts.

c. Place batteries into battery compartment.
d. Reinstall battery compartment cover.

TEST CONNECTORS

• The gateway to your vehicle's onboard computer.

Ford equips its vehicles with special Test Connectors that

make it possible to connect specialized testing equipment that
communicates with the vehicle's onboard computer.
Ford's vehicle test connectors are usually dark in color
(BLACK or GREY) and found under the hood. Sometimes they
have a plastic cover over them or are labeled EEC Test. The
connectors can be found in the following general locations in
the engine compartment:

6-PIN 6-PIN

SINGLE
PIN

EEC-IV TEST CONNECTOR MCU TEST CONNECTOR

• Near the front corner (right or left).

• Near the fender well (right or left).
• Near the fire wall (right or left).

CONNECTING THE FORD CODE READER TO THE

VEHICLE’S TEST CONNECTOR(S)
NOTE: The Code Reader is designed to match the computer's
test connector. When properly connected, the test connector
should match the pre-molded guides around the Code Reader
pins (as shown on next page).
Forcing the test connector onto the Code Reader improperly
may result in damage to the Code Reader and possible damage
to the vehicle's computer system.

Chapter 3 18
About the Ford Code Reader
FUNCTIONS OF THE FORD CODE READER 3
■ For the EEC-IV Computer System (most vehicles built
after 1984) connect the Code Reader to BOTH.
1. large, six pin female con-
nector with molded housing EEC-IV
TEST
2. small, single pin female CONNECTOR
connector
NOTE: 1988 and newer vehicles
may have more than one similar
connector for other systems (i.e.
CODE
Anti-Lock Brakes), only the READER
connector with an extra single
pin is the correct test connector
for computer service codes use. If
you have any questions about the MCU
TEST
correct connector please refer to CONNECTOR
your vehicle's service manual for
detailed information.
■ For the MCU System (most
vehicles built between 1981-
CODE
1983) connect the Code READER
Reader to the six pin female
connector only.

Optional Extension Cable

FORD
For one person operation, a 6'
optional extension cable for test
connection is available through your
local store or service department.
The extension cable allows you to do
all the code reading without the help
of another person.

FUNCTIONS OF THE FORD CODE READER

The Ford Digital Code Reader is a diagnostic tool that is
specially designed to connect to the vehicle's test Connector(s)
to communicate with the vehicle's computer.
The Code Reader does not generate codes. The Code Reader
serves as a “key” that links to, and opens communication with
the vehicle's computer to prompt the computer to perform Self
Tests, and to receive test results or retrieve codes.

19 Chapter 3
 About the Ford Code Reader
3 FUNCTIONS OF THE FORD CODE READER

The vehicle's computer generates and assigns fault codes

whenever it detects a problem in any of the various systems
that it monitors and/or controls. Once the Code Reader is
connected to the vehicle's Test Connector(s), the user can
signal the computer to perform the Self-Tests (by pressing the
TEST/HOLD button). The computer then starts performing a
Self Test of all the components and/or circuits it controls. The
results of the tests are sent to the code reader (as numerical
codes) to help the repairperson pinpoint a particular problem
in any of the computer control systems.
This Code Reader is designed to retrieve Diagnostic Trouble
Codes from Ford EEC-IV and MCU systems only.

Code Reader Controls and Indicators

2 1

MEMORY ON/ OFF

TEST/ HOLD

6 4

5
FORD LINCOLN MERCURY
Domestic vehicles 1981 to 1995

1. Code Reader Connector - Connects to the vehicle's six-

pin Test Connector (the six-pin test connector is used on
both MCU and ECC-IV systems).
2. Code Reader Connector - Connects to the vehicle's
single-pin Test Connector. (the single-pin Test Connector
is used on EEC-IV systems only; MCU systems are not
equipped with single pin test connectors).
3. LCD Display - Displays test results, Diagnostic Trouble
Codes and Code Reader functions.
4. ON/OFF Button - Turns the code reader On and Off.
5. TEST/HOLD Button: Toggles between TEST and HOLD
functions.

Chapter 3 20
About the Ford Code Reader
FUNCTIONS OF THE FORD CODE READER 3
6. MEMORY Button - When pressed, displays on demand,
one at a time, the retrieved Diagnostic Trouble Codes that
are saved in the Code Reader's memory (the Code Reader
memory has the capacity to store up to 12 retrieved
numeric Diagnostic Trouble Codes).

Display Functions

1 2 3

CYL ORC

1. CYL Icon: When visible, this icon indicates that the

number shown on the the Code Reader's display is a
cylinder identification code. Cylinder codes identify the
number of cylinders of the engine under test. Cylinder
identification is only displayed when performing a KOER
Self Test.
2. BATTERY Icon: When visible, this icon indicates that
the Code Reader's internal batteries are low. Batteries
should be replaced before performing any tests.
3. O, R, and C Icons: These icons indicate the type of test
being performed, and indicate if the code being received is
a KOEO, KOER or CM code:
O = Key On Engine Off (KOEO) Test/code
R = Key On Engine Running (KOER) Test/code
C = Continuos Memory (CM) code
These icons also identify the "code type" when viewing
Diagnostic Trouble Codes that are saved in the Code
Reader's memory.

21 Chapter 3
 About the Ford Code Reader
3 FUNCTIONS OF THE FORD CODE READER

4. "FLASHING" SQUARE Icon: This icon flashes when the

Code Reader receives Diagnostic Trouble Codes from the
vehicle's computer. The icon flashes each time a code is
received; the code is then shown on the Code Reader’s
display.
5. LINK Icon: When visible, this icon indicates that the
Code Reader is linked to the vehicle's computer, and the
computer is in test mode.
6. Diagnostic Trouble Code Display Area: Displays the
Diagnostic Trouble Code number. Each fault is assigned a
code number that is specific to that fault.

Chapter 3 22
Retrieving Codes
OVERVIEW OF FAULT CODES 4
OVERVIEW OF FAULT CODES
IMPORTANT: Retrieving and utilizing Diagnostic Trouble
Codes (DTC's) for troubleshooting vehicle operation problems is
only one part of an overall diagnostic strategy. Never replace
a part based only on the Diagnostic Trouble Code Definition.
Always consult the vehicle's service manual for more detailed
testing instructions. Each DTC has a set of testing procedures,
instructions and flow charts that must be followed to confirm
the exact location of the problem. This type of information is
found in the vehicle's service manual.
a. Fault Codes are called "Diagnostic Trouble Codes" (DTCs),
"Trouble Codes", “Fault Codes” or "Service Codes" (these
terms are used interchangeably throughout this manual).
These numeric codes are used to identify a problem in any
of the systems that are monitored by the vehicle's on-
board computer.
b. Each Fault Code is assigned a message that identifies the
circuit, component or system area where the problem was
detected.
c. Ford Diagnostic Trouble Codes are composed of two- or
three-digit numbers.
■ Most early model Ford vehicles (up to 1991) use a two-
digit code system.
■ Most late model Ford vehicles (1992 to 1995) use a
three-digit code system.
The computer records codes for three types of
conditions:
1. It records Fault Codes for problems that are present at the
time the Self-Tests are performed (the Code Reader is
used to place the vehicle's computer in Self-Test Mode; the
procedures are described in detail later in this manual).
These types of codes are usually called "Hard Codes".
Hard Codes will make the check engine light or
Malfunction Indicator Lamp (MIL), if equipped, on the
dash to come on and stay on solid.
2. It records and saves Fault Codes for "Intermittent
Problems" (not applicable to MCU systems). These
problems come and go intermittently. Intermittent Fault
Codes may cause the Check Engine/Malfunction Indicator
Lamp (MIL) light to flicker on dash.

23 Chapter 4
 Retrieving Codes
4 OVERVIEW OF FORD CODE RETRIEVAL PROCESS

3. It records and retains in its memory (not applicable to

MCU systems) a record of faults that occurred in the past
but are no longer present. The vehicle's computer keeps
these Fault Codes in its memory for a specific period of
time (40 Warm Up cycles* for most fault Codes, 80 Warm
up cycles for others) even if the problems that caused
these codes to be set in the first place are no longer
present.
*Warm-up Cycle - A Warm-up Cycle is defined as vehicle
operation (after an engine off period) where the engine
temperature rises at least 40°F (22°C) from the
temperature present when the vehicle was first started,
and the engine temperature reaches at least 160°F (70°C).
NOTE: The Code Reader does not generate codes. The Code
Reader serves as a “key” that links to, and opens
communication with the vehicle's computer to prompt the
computer to perform Self Tests, and to receive test results or
retrieve codes.

OVERVIEW OF FORD CODE RETRIEVAL PROCESS

Ford’s computer self-diagnostic system is divided into three
main sections: 1. "Key On Engine Off" (KOEO) Self Test, 2.
"Continuous Memory" (CM) Self-Test and 3. "Key On Engine
Running" (KOER) Self Test. These Self-Tests are specially
designed to monitor and/or test the various components and
circuits that are controlled by the vehicle's computer, and to
save and/or transmit diagnostic test results to the Code
Reader in the form of numerical fault codes.
• The “Continuous Memory” Self Test is designed to run
continuously whenever the vehicle is in normal operation.
If a fault is detected by the “Continuous Memory” Self
Test, a fault code is saved in the vehicle's computer
memory for later retrieval.
NOTE: Continuous Memory codes only apply to EEC-IV
systems and are retrieved during the KOEO Self Test.
• Ford designed its On-Board Diagnostic Self Tests in such
a way that in order to properly diagnose a problem, you
must performed all the Self Tests, in the proper sequence.
As described above, some tests are designed to detect
problems only when the vehicle is in normal operation,
some tests are designed to activate components and detect
problems only with the Key On and Engine Off, and other

Chapter 4 24
Retrieving Codes
KOEO TEST PROCEDURES (EEC-IV SYSTEMS) 4
tests are designed to activate components and test their
operation only with the Key On and Engine Running. Do
not take short cuts. If you fail to perform a test, or you
perform a test out of sequence, you might miss a problem
that is only detected during that particular test procedure.
To properly receive Diagnostic Trouble Codes from the
Ford computer control system, perform the Self Tests in
the following order:
1. Key On Engine Off (KOEO) Self Test
2. Ignition Timing Check (vehicle Ignition Timing System
must be working properly before the KOER Self Test can
be performed)
3. Key On Engine Running (KOER) Self Test
IMPORTANT:
• To retrieve Diagnostic Trouble Codes from EEC-IV
Systems proceed to the next section below.

• To retrieve Diagnostic Trouble Codes from MCU systems

proceed to page 66.

KEY ON ENGINE OFF (KOEO) TEST PROCEDURES

(EEC-IV SYSTEMS)
NOTE: During the KOEO Self Tests two groups of codes will be
sent to the Code Reader by the vehicle’s computer.
• The first groups of codes sent to the Code Reader are called
"KOEO Self Test codes",

• followed by the second group called "Continuous Memory

Codes".
NOTE: Before the computer sends the second group of codes to
the Code Reader, it first sends a “separator code” (code 10) to
separate the first group of codes from the second group.
• Always observe safety precautions before and during
testing process.

• ALWAYS check Code Reader battery before retrieving

fault codes.

• Fix any known mechanical problems before this test.

1. Warm-up engine to normal operating temperature before
performing this test.
2. Turn ignition off.

25 Chapter 4
 Retrieving Codes
4 KOEO TEST PROCEDURES (EEC-IV SYSTEMS)

3. With Code Reader off, connect to the vehicle's test

connectors (see page 18 for test connector location).
■ Both the large and small connectors must be
connected.
4. If your vehicle is equipped with one of the following
configurations, perform the added procedures as described
below.
■ For 4.9L engines with standard transmission: press
and hold the clutch until all Codes are sent (Steps 4 to
10).
■ For 7.3L diesel engines: press and hold accelerator
until all codes are sent (Step 4 to 10).
■ For 2.3L turbo engines with octane switch: put switch
in premium position.
NOTE: Do not press throttle or brake, or move steering
wheel, during this test unless instructed.
5. Turn ignition on. DO NOT START THE ENGINE.
WARNING: Keep away from any potentially moving parts.
6. Press and release the ON/OFF
button to turn the Code Reader
"ON".
■ Three zeros should be
visible on the Code Reader
display at this time.

7. Press and release the

TEST/HOLD button to put the
Code Reader in Test Mode.
■ When the code reader is put in test mode it signals
the vehicle's computer to start performing the Self-
Test. The display will show a "Triangle" icon on the
lower right hand corner of the display to indicate that
the Code Reader is linked to the vehicle's computer
and is in test mode.
NOTE: As soon as the TEST/HOLD button is pressed
the vehicle's computer enters the Self Test mode.
Clicking sounds will be heard coming from the engine.
This is normal. It indicates that the vehicle's computer
is activating relays, solenoids, and other components
to check their operation.

Chapter 4 26
Retrieving Codes
KOEO TEST PROCEDURES (EEC-IV SYSTEMS) 4
WARNING: On some vehicles equipped with an
Electric Cooling Fan, the computer activates the
cooling fan to check its operation. To avoid
injury, keep hands or any part of your body a
safe distance from engine during the test.
8. After 6 to 10 seconds (it may take longer on some vehicles)
the computer will start sending the KOEO Self Test
results to the Code Reader in the form of numerical codes.
NOTE: Most Ford EEC-IV vehicle computers up to 1991
use a two-digit code system. From 1991 to 1995 most use a
three-digit code system.
■ A square icon (on the right-
hand side of the screen)
O
displays and flashes each
time the Code Reader
receives a code. The code is
then shown on the Code
Reader's display.
■ A small "O" is shown in the upper right-hand corner
of the display to indicate that the code being received
is a KOEO Self Test fault code.
NOTE: Each code is repeated two times.
9. If no problems are found during
the KOEO Self Test, the
O
computer sends a “pass code”
(code 11 or 111) to the Code
Reader.
■ Code 11 or 111 indicates that
O
all the relays and actuators
(and their related circuits)
that were tested are OK, and
no faults were found.
■ If the Code Reader fails to display codes, consult the
troubleshooting guide on pages 75 and 76.
10. Approximately six to nine seconds
after the Code Reader receives
the last KOEO Self Test fault
code(s), a “separation code” (code
10) is sent to the Code Reader.

27 Chapter 4
 Retrieving Codes
4 KOEO TEST PROCEDURES (EEC-IV SYSTEMS)

■ Code 10 is not a fault code. Code 10 is a “separation

code” used to separate the first group of codes (KOEO
Self Test Codes) from the Continuous Memory group
of codes.
■ Code 10 also serves as an indication to the user that
the vehicle's computer has completed the first part of
the KOEO Self Test, and that the next groups of codes
to be displayed are Continuous Memory codes.
11. Approximately nine seconds after
the Code Reader receives the C
“separation code” (code 10), it
begins retrieving any Continuous
Memory codes that are present in
the vehicle's computer memory.
■ A small "C" is shown in the upper right-hand corner
of the display to indicate that the codes being
retrieved are Continuous Memory codes.
■ If no Continuous Memory codes are present in the
vehicle's computer memory, The code reader will
display a “pass code” (code 11 or 111).
12. After all the KOEO Self Test Codes and Continuous
Memory codes have been received by the Code Reader
(wait until the flashing square icon no longer appears on
the display for 30 consecutive seconds to ensure that all
the codes have been retrieved), press the ON/OFF button
to turn the Code Reader off, disconnect the Code Reader
from the vehicle's test connectors, and turn the ignition
off.
■ The codes retrieved are now stored in the Code
Reader's memory.
13. To view codes stored in the Code Reader's memory, press
the ON/OFF button to turn the Code Reader on, then
press and release the MEMORY button; the first stored
code will display. Continue pressing and releasing the
MEMORY button to scroll through the stored codes until
all the codes have been displayed.
NOTE: All retrieved codes will stay in the Code Reader's
memory and will only clear from the Code Reader's
memory if the Self Test procedure is performed again
(codes from a prior test will clear automatically when new
Self Test is performed) or if batteries are removed from the
Code Reader.

Chapter 4 28
Retrieving Codes
KOEO TEST PROCEDURES (EEC-IV SYSTEMS) 4
14. If any KOEO Self Test Fault Codes were retrieved:
■ Refer to page 46 for "Fault
Code Definitions for EEC-IV
C
Systems". Match the codes
retrieved with the codes
shown in the Fault Code
Definition list to determine
the fault.
■ Use the code definitions as a guide, and follow the
manufacturer's service procedures in the vehicle's
service repair manual to troubleshoot and repair
faults.
■ All KOEO Self Test codes (except Continuous Memory
Codes) that are received by the Code Reader during
the KOEO Self test represent problems that are
present now (at the time the test is performed). The
related vehicle problems that cause these codes to set
must be repaired using the procedures described in
the vehicle's service repair manual.
■ Do not service "Continuous Memory" codes at this
time. See IMPORTANT note at end of KOEO
procedure for more details.
15. After all repairs have been completed, repeat the KOEO
Self Test. If a “pass code” (code 11 or 111) is received, it
indicates that the repairs were successful, and you can
proceed to perform Ignition Timing Check (see page 30). If
a “pass code” (code 11 or 111) is not received, the repair
was unsuccessful. Consult the vehicle's service manual
and recheck repair procedures.
DO NOT PROCEED TO "IGNITION TIMING CHECK
PROCEDURE " UNTIL A “PASS CODE” (CODE 11 OR
111) FOR "KOEO SELF TEST" IS OBTAINED.
IMPORTANT: Before Continuous Memory codes can be serviced,
both the KOEO and the KOER Self-Tests must pass (a code 11
or 111 is obtained). After both of these tests have passed, erase
the vehicle's computer memory (see page 37), take the vehicle
for a short drive, then repeat the KOEO Self test. If any
Continuous Memory faults are present, service them at this
time. Refer to page 46 for "Fault Code Definitions for EEC-IV
Systems", and consult the vehicle's service repair manual for
servicing Continuous Memory Fault Codes.

29 Chapter 4
 Retrieving Codes
4 ENGINE TIMING CHECK (EEC-IV SYSTEMS)

ENGINE TIMING CHECK (EEC-IV SYSTEMS)

IMPORTANT: Before performing the KOER Self Test, the
vehicle’s Ignition Base Timing and the computer’s ability to
electronically control timing advance must be checked for
proper operation. Maladjustment of ignition timing, or a
problem in the advance circuit, might generate false fault codes
when performing the KOER Self Test that would cause the test
to be invalid. Use the following procedures to check for proper
ignition timing and to verify the computer’s ability to
electronically advance ignition timing.
This procedure is used to check for proper ignition timing, and
to verify the computer's ability to electronically advance
ignition timing.
• For 1992 and older vehicles, the Code Reader can be used
in combination with a timing light to check ignition timing
and the vehicle's computer ability to advance ignition
timing. Follow the procedures in paragraph "A".

• For 1993 and newer vehicles, follow procedures in

paragraph "B".
A. Timing Procedures for 1992 and Older Vehicles (excluding
diesel engines)
• Always observe safety precautions before and during Self-
Test.

• ALWAYS check Code Reader battery before retrieving

fault codes.

• A timing light is required to perform this test.

• The vehicle must pass the KOEO test before performing

this test.
1. Turn ignition off.
2. Turn the Code Reader off (press the ON/OFF button, as
necessary), then connect the Code Reader to the vehicle's
test connectors.
■ Both the large and small connectors must be
connected.
3. Start the engine.
4. Press and release the ON/OFF button to turn the Code
Reader "ON".

Chapter 4 30
Retrieving Codes
ENGINE TIMING CHECK (EEC-IV SYSTEMS) 4
5. Press and release the TEST/HOLD button to put the
Code Reader in test mode. The vehicle's computer will
perform a Key On Engine Running Self test.
■ A square icon (on the right-hand side of the screen)
displays and flashes each time the Code Reader
receives a code. The code is then shown on the Code
Reader's display.
6. Wait until all codes have been sent (the flashing square
icon no longer appears) and, without disconnecting or
turning the Code Reader off, proceed to step 7.
NOTE: Do not concern yourself with the KOER test results
or any fault codes received at this time. The purpose of
briefly performing the KOER test is to put the computer
into an "Ignition Timing Check mode". This mode allows
you to test the ability of the vehicle's computer to
electronically control/advance ignition timing. Once the
timing check confirms that ignition timing is functioning
correctly, you can properly perform the KOER Self Test.
7. The vehicle's computer is programmed to advance ignition
timing 20° (+/- 3°) above the vehicle's “base timing” value,
and to freeze this setting for two minutes from the time
the last KOER code is received by the Code Reader. This
allows the user to check the computer's ability to advance
ignition timing.
■ Within this two-minute period, (remember, timing
degrees will remain fixed for only two minutes after
the last KOER code is received by the Code Reader),
check the ignition timing with a timing light and
ensure that it is 20° above the specified base timing
value (+/- 3° ).
Example: If base timing specification is 10° BTDC,
the acceptable timing light reading should be in the
range of 27° to 33° BTDC.
NOTE: Base timing specifications can be found on the
Vehicle Emission Control Information (VECI) decal. The
decal is located under the hood or near the radiator. If the
VECI decal is missing or damaged, refer to your vehicle's
service manual for specifications.
8. If timing light readings are not within the acceptable range,
base timing may be out of adjustment, or the computer may
have problems with the timing advance circuit.

31 Chapter 4
 Retrieving Codes
4 KOER SELF TEST (EEC-IV SYSTEMS)

■ Turn the engine off and disconnect the Code Reader

from the test connectors. Refer to the vehicle's service
manual for instructions on adjusting and/or repairing
ignition timing.
9. If timing light readings are within the acceptable range,
base timing and the vehicle's computer ability to advance
timing are working properly.
■ Turn engine off and disconnect the Code Reader from
test connectors. Proceed to page 32 and perform the
KOER Self Test.

B. Timing Procedures for 1993 And Newer Vehicles (excluding

diesel engines)

Due to the complexity and large variation of Ford 1993 and

newer models with computer-controlled ignition timing
systems, timing adjustment and/or checking procedures vary
widely from one model to the next. Refer to the vehicle’s service
manual for procedures to check and adjust timing. DO NOT
ATTEMPT TO ADJUST TIMING WITHOUT MANUFAC-
TURER’S SPECIFICATIONS AND PROCEDURES.

KEY ON ENGINE RUNNING (KOER) SELF TEST

(EEC-IV SYSTEMS)
IMPORTANT:
• The KOEO Self Test (page 25) must be performed first, and
a “pass code” (code 11 or 111) must be obtained before
performing the KOER Self Test; otherwise, results of the
KOER Self Test may be invalid.

• Ignition timing and timing advance must be operating

properly in order for the KOER Self Test results to be
considered valid. Perform an Ignition Timing Check (page
31) before performing the KOER Self Test.

• Always observe all safety precautions before and during

the testing process.

• ALWAYS check the code reader's batteries before the test.

Chapter 4 32
Retrieving Codes
KOER SELF TEST (EEC-IV SYSTEMS) 4
1. Warm up the vehicle to normal operating temperature.
■ Start the engine, increase engine speed to 2000 RPM,
and maintain engine speed for approximately two to
three minutes. In most cases, this is sufficient to
allow the engine to warm up to normal operating
temperature.
NOTE: Failure to warm engine to normal operating
temperature before performing KOER test might result in a
false Fault Code being sent to the code reader.
2. Turn ignition off.
3. Turn the Code Reader off (press the ON/OFF button, as
necessary), then connect the Code Reader to the vehicle's
test connectors.
■ Both the large and small connectors must be
connected.
4. Turn ignition on and start the engine.
5. Press and release the ON/OFF
button to turn the Code Reader
"ON".
■ Three zeros should be visible
on the display at this time.
6. Press and release the TEST/HOLD button to put the
Code Reader in Test Mode.
■ A square icon (on the right-
hand side of the screen)
displays and flashes each R

time the Code Reader

receives a code. The code is
then shown on the Code
Reader’s display.
■ A small “R” is shown in the upper right-hand corner
of the display to indicate that the code being received
is a KOER Self Test Fault Code.
7. The first code displayed by the
code reader is the Cylinder
Identification (ID) Code. CYL R

■ The cylinder ID code identi-

fies the number of cylinders
of the vehicle that is under
test.

33 Chapter 4
 Retrieving Codes
4 KOER SELF TEST (EEC-IV SYSTEMS)

NOTE: If code 98 or 998 dis-

R
plays instead of a cylinder ID
code, the vehicle is operating in
"Failure Mode". The computer
goes into failure mode when it
detects a signal from a sensor
R
that indicates the sensor has
failed and is completely out of
specifications. The computer
substitutes a fixed signal value
for the failed sensor to keep the vehicle running. Failure
mode codes 98 or 998 are usually accompanied by one or
more Diagnostic Trouble Codes that indicate the failed
sensor. A vehicle operating in failure mode is operating at
a minimal level, and the faults that are causing these
Diagnostic Trouble Codes to set must be repaired as soon
as possible.
8. Check your vehicle's service manual to see if your vehicle
is equipped with a Power Steering Pressure Switch, Brake
On/Off (BOO) Switch and/or an Overdrive Cancel Switch.
If your vehicle is equipped with these features, perform
the following immediately after retrieving the Cylinder ID
code (step 7).
NOTE: If you are unsure of your vehicle's equipment, it is
recommended that you perform these procedures anyway.
■ If your vehicle has a Power Steering Pressure Switch
(PSPS), turn the steering wheel a half turn; wait
three to five seconds, then release. The computer
checks for proper variations in power steering
pressure during this procedure. Failure to perform
this procedure will generate a Fault Code.
■ If your vehicle has a Brake On/Off (BOO) Switch, step
on the brake pedal once, and release. The computer
checks the Brake On/Off Switch for proper operation
during this procedure. Failure to perform this
procedure will generate a Fault Code.
■ If your vehicle has an Overdrive Cancel Switch (OCS),
turn the switch on and off once. Failure to perform
this procedure will generate a Fault Code.
9. Thirty to sixty seconds after the cylinder ID code is re-
ceived, code 10 may display (code 10 is not applicable to all
vehicles). If a code 10 is displayed, quickly press the accel-
erator pedal to the floor and release, then proceed to step
10. If code 10 is not displayed proceed directly to step 10.

Chapter 4 34
Retrieving Codes
KOER SELF TEST (EEC-IV SYSTEMS) 4
■ Code 10 is not a fault code.
The vehicle's computer uses
code 10 to signal the Code
Reader operator to perform
a Wide Open Throttle
(WOT) test (quickly press
and release the accelerator
pedal).
This procedure is called the Dynamic Response
Check. The computer uses this brief Wide-Open
Throttle (WOT) test to verify the operation of the
Throttle Positioning, Mass Airflow, Manifold Absolute
Pressure and Knock Sensors.
■ If you fail to press the accelerator to the floor as
instructed in step 9, a Dynamic Test Failure Code
may be generated.
10. After the dynamic test is completed (if applicable), the
vehicle computer proceeds to test the actuators, switches,
relays and their related circuits. If any problems are detected
in any of these components or circuits as they are tested, a
Diagnostic Trouble Code is sent to the Code Reader.
NOTE: Each code is repeated two times.
11. If no problems are found during
the KOER Self Test, the computer O
sends a “pass code” (code 11 or
111) to the Code Reader.
■ Code 11 or 111 indicates that
all the relays and actuators
O
and their related circuits
that were tested during the
KOER Self-Test are OK, and
no faults were found.
NOTE: Most Ford EEC-IV vehicle computers up to 1991
use a two-digit code system. From 1991 to 1995 most use a
three-digit code system.
12. After all the KOER Self Test codes are received by the
Code Reader (wait until the flashing square icon no longer
appears on the screen for 30 consecutive seconds to ensure
that all the codes have being retrieved), turn the Code
Reader off, turn the engine off, and disconnect the Code
Reader from the vehicle's test connectors. The codes
received are now stored in the code reader's memory.

35 Chapter 4
 Retrieving Codes
4 KOER SELF TEST (EEC-IV SYSTEMS)

13. To view codes stored in the Code Reader's memory, press

the ON/OFF button to turn the Code Reader on, then
press and release the MEMORY button; the first stored
code will display. Continue pressing and releasing the
MEMORY button to scroll through the stored codes until
all the codes have been displayed.
NOTE: All retrieved codes will stay in the Code Reader's
memory and will only clear from the Code Reader's
memory if the Self Test procedure is performed again
(codes from a prior test will clear automatically when new
Self Test is performed) or if batteries are removed from the
Code Reader.
14. If any KOER Self Test Fault Codes were received:
■ Refer to page 46 for "Fault
Code Definitions for EEC-IV
R
Systems". Match the codes
retrieved with the codes
shown in the Fault Code
Definition list to determine
the fault.
■ Use the code definitions as a guide, and follow the
manufacturer's service procedures in the vehicle's
service repair manual to troubleshoot and repair faults.
■ All KOER codes that are received by the Code Reader
during the KOER Self Test represent problems that
are present now (at the time the test is performed).
The related vehicle problems that caused the codes to
be set must be repaired using the procedures
described in the vehicle's repair manual.
15. After all repairs have been completed, repeat the KOER
Self Test.
■ If a “pass code” (code 11 or 111) is received, it
indicates that the repairs were successful and all the
related systems are working properly.
■ If a “pass code” (code 11 or 111) is not received, the
repair was unsuccessful. Consult the vehicle's service
manual and recheck repair procedures.

Chapter 4 36
Retrieving Codes
ERASING CODES FROM EEC-IV SYSTEMS 4
ERASING CODES FROM EEC-IV SYSTEMS

IMPORTANT: Continuous Memory Codes are the only ones that

are saved in the vehicle’s computer long-term memory. KOEO
and KOER Self Test fault codes represent problems that are
present at the time these tests are performed and are detected
by the computer only while the problem is present. KOEO and
KOER codes are not saved in the vehicle’s computer memory,
and if the problem that caused these faults to set is repaired,
these codes will no longer be present when the Self Tests are
performed.
This procedure clears Continuos Memory codes from the
vehicle's computer memory.
• Erase codes only when all repairs have been
completed.

• Always observe safety precautions before and during

testing process.

• ALWAYS check Code Reader battery before retrieving

fault codes.
1. Turn ignition off.
2. Turn the Code Reader off (press the ON/OFF button, as
necessary), then connect the Code Reader to the vehicle's
test connectors.
■ Both the large and small connectors must be
connected.
3. Turn on ignition. DO NOT START THE ENGINE.
WARNING: Keep away from any potentially moving
parts.
4. Press and release the ON/OFF button to turn the Code
Reader "ON".
■ Three zeros should be visible on the display at this
time.
5. Press and release the TEST/HOLD button to put the
Code Reader in Test Mode.
■ When the Code Reader is put into test mode, it
signals the vehicle's computer to start performing the
Self-Test. The display will show a "Triangle" icon on
the lower right hand corner of the display to indicate
that the Code Reader is linked to the vehicle's
computer and is in test mode.

37 Chapter 4
 Retrieving Codes
4 ADDITIONAL TESTS FOR EEC-IV SYSTEMS

NOTE: As soon as the TEST/HOLD button is pressed

the vehicle's computer enters the Self Test mode.
Clicking sounds will be heard coming from the engine.
This is normal. It indicates that the vehicle's computer
is activating relays, solenoids, and other components
to check on their operation.
WARNING: On some vehicles equipped with an
Electric Cooling Fan, the computer activates the
cooling fan to check its operation. To avoid
injury, keep hands or any part of your body a
safe distance from engine during the test.
6. After 6 to 10 seconds (it may take longer on some vehicles)
the computer will start sending the KOEO Self Test
results to the Code Reader in the form of numerical codes.
■ A square icon (on the right-hand side of the screen)
displays and flashes each time the Code Reader
receives a code. The code is then shown on the Code
Reader's display.
7. As soon as the code reader
starts receiving codes, press and
release TEST/HOLD button to
put Code Reader on HOLD. MEMORY ON/ OFF

■ The Code Reader must be TEST/ HOLD

put on HOLD while it is

retrieving codes in order for FORD
E C M

LINCOLN
A B S

Domestic vehicles 1981 to 1995

MERCURY

“Continuous Memory” codes

to be erased from the
computer's memory.
8. "Continuous Memory" codes are erased.
9. Turn off the ignition and disconnect the Code Reader from
the test connectors.

ADDITIONAL TESTS FOR EEC-IV SYSTEMS

NOTE: These tests are additional, supplemental tests, and are
not needed to retrieve Diagnostic Trouble Codes. Ford has
included them to further assist the technician / do-it-yourselfer
in the troubleshooting of vehicle problems.

Chapter 4 38
Retrieving Codes
ADDITIONAL TESTS FOR EEC-IV SYSTEMS 4
Relay and Solenoid Test (Output State Check)
The "Output State Check " is a special program in the vehicle's
computer that allows the user to energize (turn ON) and de-
energize (turn OFF), on command, most of the actuators
(relays and solenoids) that are controlled by the computer.
• Use this test to check computer output voltages and
relay/solenoid operation.
NOTE: The fuel injectors and fuel pump are not energized
during this test.
• The Output Check Mode is activated immediately after
the Key On Engine Off (KOEO) Self Test is performed.
1. Perform the Key On Engine Off (KOEO) Self Test,
steps 1 through 11 (refer to page 25 for procedures).
2. Wait until the Code Reader retrieves all the KOEO Self
Test and Continuous Memory codes.
■ The flashing square icon no longer appears on the
display when all the codes have been retrieved.
3. Immediately after all Continuous Memory codes have
been retrieved, step on the accelerator pedal once, then
release. This activates the Output State Check and
energizes most of the actuators (relays and solenoids)
that are controlled by the vehicle's computer.
NOTE: If your vehicle is equipped with an Integrated
Vehicle Speed Control, disconnect the vacuum supply hose
from the speed control servo before pressing the accelerator.
Reconnect vacuum hose after test.
■ The square icon will appear and stays on solid on the
right hand side of the code reader's display to indicate
that the Actuators are energized.
4. To de-energize the actuators, press the accelerator pedal
once and release. The square will disappear, indicating
that the actuators are de-energized.
■ The procedure can be repeated as many times as
desired by pressing and releasing the accelerator
pedal to energize and de-energize the Actuators.
5. Consult the vehicle's service manual for a list of all the
actuators (solenoids and relays) controlled by the
computer that apply to the vehicle under test, and which
actuators should energize and de-energize when
performing the "Output State Check". All applicable
actuators should be on when energized and off when de-
energized.

39 Chapter 4
 Retrieving Codes
4 ADDITIONAL TESTS FOR EEC-IV SYSTEMS

■ The vehicle’s computer sends a voltage output signal

or a ground signal to energize the actuators. If an
actuator is not responding to the Output State Check,
follow the procedures described in the vehicle's service
manual to check computer actuator output circuit
voltages and/or grounds.
6. After performing the Output State Check, turn off the
ignition and disconnect the Code Reader from the test
connectors.

Cylinder Balance Test

(Vehicles equipped with Sequential Electronic Fuel
Injected (SEFI) systems only)
The Cylinder Balance Test assists in finding a weak or non-
contributing cylinder. The computer shuts off fuel (cuts off
power to injectors) to each cylinder, in sequence, and monitors
for RPM changes (drop). Based on this information, the
computer determines if all the cylinders are contributing power
equally (for proper engine operation), or if some cylinders are
only contributing partially or not contributing at all.
SEFI Introduction
Sequential Electronic Fuel Injection (SEFI) belongs to a family
of fuel injection systems called "Multiport/Multipoint Fuel
Injection".
Multiport (MFI) fuel injection systems contain one fuel injector
per cylinder, and the vehicle's computer electronically controls
their operation. On some multiport fuel injection system, the
injectors all fire at the same time and at every engine
revolution. On other systems the injectors fire in groups and/or
at every other engine revolution.
What distinguishes Sequential Electronic Fuel Injection
systems from other multiport fuel injection systems is that
each injector is independently energized and fires sequentially
one after the other in the proper firing order. This gives the
vehicle computer more control to cut the fuel to one injector at
a time (this can't be accomplished on the other systems
because they fire in groups of two or more injectors).
The computer can be put in "Cylinder Balance Test Mode" by
performing the KOER Self Test, waiting until all the KOER
codes have been transmitted to the Code Reader, and then
lightly taping the accelerator (follow the Cylinder Balance Test
procedures, following).

Chapter 4 40
Retrieving Codes
ADDITIONAL TESTS FOR EEC-IV SYSTEMS 4
Cylinder Balance Test Procedure
• Always observe safety precautions before and during
testing process.

• ALWAYS check Code Reader battery before retrieving

fault codes.

• The vehicle must pass the KOEO test before performing

this test.
1. Turn ignition off.
2. Turn the Code Reader off (press the ON/OFF button, as
necessary), then connect the Code Reader to the vehicle's
test connectors.
■ Both the large and small connectors must be
connected.
3. Turn the ignition on and start the engine.
4. Press and release the TEST/HOLD button to put the
Code Reader in test mode. The vehicle's computer will
perform a Key On Engine Running Self test.
■ A square icon (on the right-hand side of the screen)
displays and flashes each time the Code Reader
receives a code. The code is then shown on the Code
Reader's display.
NOTE: Each code is repeated twice
5. Wait until all the codes are sent (the flashing square icon
no longer appears), then, without disconnecting or turning
Code Reader or the engine off, proceed to step 6.
NOTE: Do not concern yourself with the KOER test results
or any KOER fault codes received at this time. The purpose
of briefly performing the KOER test is to put the computer
into the "Cylinder Balance Test Mode"; this mode will
allow the user to determine if all the cylinders are
contributing equally to vehicle operation.
6. After all the KOER codes have been received by the Code
Reader, lightly press the accelerator, about one quarter of
the way down, then release.
■ For 1986 models ONLY: Fully press accelerator
once and release.

41 Chapter 4
 Retrieving Codes
4 ADDITIONAL TESTS FOR EEC-IV SYSTEMS

■ The computer is now in Cylinder Balance Test Mode,

and will start cutting fuel to each cylinder in sequence
to determine if all the cylinders are contributing
equally. It may take up to five minutes before the
test results are transmitted to the Code Reader.
7. After the computer finishes performing the Cylinder
Balance Test, the test results are sent to the Code Reader
in the form of two digit codes.
■ The computer compares the power contribution that
each cylinder makes to engine operation. If a cylinder
is not contributing at the same level as the other
cylinders, the computer sends a two digit code to the
Code Reader that identifies that particular cylinder
(see code description below).
■ If all cylinders are contributing equally, the computer
sends a pass code (code 90) to the Code Reader to
indicate that the system is OK, and that all cylinders
are contributing equally.
Cylinder Balance Test Code Definitions
CODE CODE DEFINITION
10 Cylinder #1 has a problem
20 Cylinder #2 has a problem
30 Cylinder #3 has a problem
40 Cylinder #4 has a problem
50 Cylinder #5 has a problem
60 Cylinder #6 has a problem
70 Cylinder #7 has a problem
80 Cylinder #8 has a problem
90 System is OK, all cylinders are
contributing equally
NOTE: The severity of an improperly contributing
cylinder may be anywhere from mild to no
contribution at all. In order for the computer to
determine the severity of an improperly contributing
cylinder, the Cylinder Balance Test may have to be
consecutively repeated up to three times

Chapter 4 42
Retrieving Codes
ADDITIONAL TESTS FOR EEC-IV SYSTEMS 4
■ The Cylinder Balance Test can be repeated by
pressing and releasing accelerator pedal (as described
in step 6, on page 41) within two minutes after the
last cylinder balance code is retrieved.
Use the A, B, C, and D examples in the "TEST
RESULTS CHART" to determine the meaning of the
test results. The chart uses the #2 cylinder as an
example, but the procedures are the same for any
cylinder.

TEST RESULTS CHART

TEST RESULTS TEST PROBLEM POSSIBLE
1st 2 nd 3rd DEFINITION INDICATION CAUSE
A 90 * * System passed System passed. •System OK
1st test All cylinders are
contributing
equally.
B 20 90 * Fails 1st test Weak cylinder, •Bad spark plug
Passes 2nd test cylinder is firing, wire or spark plug
but not contribu- •Partially clogged
ting the same as injector or injector
the others circuit problem
•Mechanical
problem - rings,
valves, etc.
C 20 20 90 Fails 1st test Same as above, but •Same as above,
Fails 2nd test condition is more but the condition
Passes 3rd test severe. is more severe.
D 20 20 20 Fails 1st test Very weak or dead •Bad spark plug
Fails 2nd test cylinder wire or spark plug
Fails 3rd test •Open or shorts on
injector circuit,
clogged injector
•Mechanical
problem - rings
valves, etc.

Test Results Chart (Examples) Explanation

A: If a code 90 is retrieved the 1st time the cylinder balance
test is performed (example A in TEST RESULTS
CHART), the system is OK, and no further testing is
required. Proceed to step 8.

43 Chapter 4
 Retrieving Codes
4 ADDITIONAL TESTS FOR EEC-IV SYSTEMS

B: If a cylinder problem code (Code 20 in example B in TEST

RESULTS CHART) is retrieved the 1st time the test is
performed, repeat the test again. If the system passes the
2nd time (Code 90) the test is performed, testing is
complete. Consult the Test Chart for “Problem Indication”
and “Possible Cause”, then proceed to step 8.
• In example B, the test results show that cylinder #2
failed the test the first time but passed the 2nd time,
indicating that #2 cylinder is firing but not
contributing the same as the other cylinders.
C: If a cylinder problem code (Code 20 in example C in TEST
RESULTS CHART) is retrieved the 1st and 2nd time the
test is performed, repeat the test for a 3rd time. If the
system passes on the third time (Code 90), testing is
complete. Consult the Test Chart for "Problem Indication"
and "Possible Cause" and proceed to step 8.
• In example C, the test results show that cylinder #2
failed the 1st and 2nd tests but passed on the 3rd test.
This indicates that the cylinder is firing but not
contributing the same as the other cylinders. The test
results also show that in example C the problem is
more severe than in example B.
D: If a cylinder problem code (Code 20 in example D in TEST
RESULTS CHART) is retrieved the 1st, 2nd and 3rd time
the test is performed, testing is complete. Consult the Test
Chart for “Problem Indication” and “Possible Cause”, then
proceed to step 8.
• In example D, the test results show that # 2 cylinder
failed the 1st, 2nd and 3rd tests. This indicates that
cylinder #2 is extremely weak or dead, and there is
very little or no power contribution to engine
operation coming from this cylinder.
8. Turn the ignition off and disconnect the Code Reader from
the test connectors. The Cylinder Balance Test results are
now in the Code Reader's memory.
9. To view the Cylinder Balance Codes stored in the Code
Reader's memory, press the ON/OFF button to turn the
Code Reader on, then press and release the MEMORY
button; the first stored code will display. Continue pressing
and releasing the MEMORY button to scroll through the
stored codes until all the codes have been displayed.

Chapter 4 44
Retrieving Codes
ADDITIONAL TESTS FOR EEC-IV SYSTEMS 4
NOTE: After the Cylinder Balance Test is done, the KOER
Test Fault Codes will be saved in the Code Reader's
memory together with Cylinder Balance fault codes. To
distinguish between the KOER codes and Cylinder Balance
codes, consult the "Cylinder Balance Test Code Description
Chart" preceeding. Cylinder Balance fault codes are two
digit codes, and are defined by the following numbers: 10,
20, 30, 40, 50, 60, 70, 80 and 90. Cylinder Balance codes
will be displayed after KOER Self-Test codes.
■ If any cylinder codes were received, use "Code
Description" and "Test Results Chart" as a guide and
consult the vehicle's service manual to perform
further testing and/or repairs.
Wiggle Test (EEC-IV Systems)

• Always observe safety precautions before and during

testing process.

• ALWAYS check Code Reader battery before retrieving

fault codes.

• Use this test to check for intermittent faults in some

circuits.
Circuits Tested:
1984 & Newer - Air Charge Temp Sensor (ACT), Barometer
Pressure Sensor (BP), Engine Coolant Temp Sensor (ECT),
Exhaust Gas Oxygen Sensor (EGO), EGR Valve Position
Sensor (EVP), Manifold Absolute Pressure (MAP), Throttle
Position Sensor (TP), Vane Air Temp Sensor (VAT)
1985 & Newer - Vane Air Flow Sensor (VAF)
1986 & Newer - Pressure Feedback EGR Sensor (PFE)
1990 & Newer - Exhaust Gas Oxygen Sensor (EGO), Ignition
Diagnostic Monitor (IDM) (DIS or Dual Plug DIS only), Idle
Tracking Switch (ITS), Mass Air Flow Sensor (MAF)
1. Turn ignition off.
2. Press and release the ON/OFF button to turn the Code
Reader "ON". Press the TEST/HOLD button to place the
Code Reader on “Hold”, then connect the Code Reader to
the vehicle's test connectors.
■ Both the large and small connectors must be
connected.
3. Turn the ignition on. DO NOT START THE ENGINE.

45 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (11 - 15)

■ For 1986 and older vehicles: Wiggle test is now

active. Proceed to step 4.
■ For 1987 and newer vehicles: Set Code Reader
switch to TEST, then HOLD, then TEST. Wiggle test
is now active. Proceed to Step 4.
4. Perform "Wiggle Test" on circuit.
■ Wiggle sensor, connector and wiring that needs to be
tested; a code will display if a fault is detected.
NOTE: On some models, service codes are lost when
the ignition is turned off.
5. Turn off ignition and disconnect Code Reader from test
connectors.
■ Consult service manual and service any fault codes
retrieved during Wiggle Test.

FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS CAR &

TRUCK
IMPORTANT: Retrieving and utilizing Diagnostic Trouble
Codes (DTC's) for troubleshooting vehicle operation problems is
only one part of an overall diagnostic strategy. Never replace
a part based only on the Diagnostic Trouble Code Definition.
Always consult the vehicle's service manual for more detailed
testing instructions. Each DTC has a set of testing procedures,
instructions and flow charts that must be followed to confirm
the exact location of the problem. This type of information is
found in the vehicle's service manual.
Test Condition Key:
O = Key Off Engine Off (KOEO) code
R = Key Off Engine Running (KOER) code
C = Continuous Memory (CM) code
TEST
CODE CONDITION FAULT CODE DEFINITION
11 O, R, C System OK
12 R RPM at idle out of range/high
13 R RPM at idle out of range/low
14 C Ignition profile pickup (PIP) circuit failure
14 C Engine RPM sensor circuit fault (Diesel)
15 O EEC (PCM) Read Only Memory (ROM) test
failed

Chapter 4 46
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (15 - 24) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
15 C Power Interruption to computer memory or
EEC (PCM) Keep Alive Memory (KAM) test
failed
15 O Read Only Memory test failed
16 O (Cars ONLY): Signal from Ignition
Diagnostic Monitor (IDM) not received
16 R RPM too low to perform HEGO (HO2S) test
16 R Idle RPM high with ISC retracted
16 R RPM above self test limit with ISC off
17 R (Cars ONLY): RPM below self-test limit
17 R Idle RPM low with ISC retracted
17 R Idle RPM high with ISC retracted
18 R SPOUT circuit open or Spark Angle Word
(SAW) circuit failure
18 C Loss of tachometer input/IDM circuit
failure / SPOUT circuit grounded
19 O Failure in EEC (PCM) internal voltage
19 R (Cars ONLY): Erratic RPM signal at idle /
too low
19 C (Cars ONLY): Cylinder Identification (CID)
sensor failure
19 O Power processor check
21 O, R Cooling Temperature sensor out of specified
range or ECT out of range
22 O, R, C Manifold Absolute Pressure (MAP) or
BARO sensor out of range
23 O, R, C (Cars ONLY): Throttle Position (TP) sensor
signal out of range
23 O, R (Trucks ONLY): Throttle Position (TP)
sensor signal out of range
23 O, R Fuel injector pump lever sensor input is out
of self test range (Diesel)
24 O, R Intake Air Charge Temperature (ACT, IAT)
sensor or Vane Air Temperature (VAT)
sensor out of range
24 C Coil #1 primary circuit failure

47 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (25 - 33)

TEST
CODE CONDITION FAULT CODE DEFINITION
25 R Knock not sensed during Dynamic
Response Test
26 O, R (Cars ONLY): Mass Air Flow (MAF) sensor
or Vane Air Flow (VAF) sensor or
Transmission Oil Temperature (TOT)
sensor out of range
26 O, R (Trucks ONLY): MAF sensor or circuit
fault (4.0L models)
26 O, R (Trucks ONLY): Transmission oil
temperature sensor fault (ex. 4.0L)
27 C (Cars ONLY): Vehicle speed sensor or
EDIS fault
27 C Coil #2 primary circuit failure
28 O, R (Cars ONLY): Vane Air Temperature
(VAT) sensor; EDIS or DIS fault
28 C Loss of primary tachometer (IDM), right
side
29 C Insufficient input from the Vehicle Speed
Sensor (VSS)
29 C Insufficient input from programmable
speedometer/odometer module
31 O, R, C (Cars ONLY): EVP or PFE circuit below
minimum voltage
31 O, R, C (Trucks ONLY): EGR valve control sensor
fault (ex. V8 models)
31 O, R (Trucks ONLY): EVAP control system
below minimum voltage
32 R (Cars ONLY): EGR valve control system
signal out of specification
32 R, C (Cars ONLY): EGR valve not seated
32 R, C (Trucks ONLY): EGR pressure feedback
fault (1985-89 models)
32 O, R, C (Cars ONLY): EVP voltage low (SONIC) or
EPT circuit voltage low (PFE)
33 R, C (Cars ONLY): EGR valve not opening
properly
33 R, C (Trucks ONLY): EGR valve fault / not
closing properly / TPS fault (Diesel)

Chapter 4 48
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (34 - 42) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
34 R (Cars ONLY): EGR valve not opening
properly
34 O, R, C (Cars ONLY): Insufficient EGR flow or
EVP voltage high (SONIC) or PFE sensor
voltage high or out of specification
34 O, R, C (Trucks ONLY): EGR control circuit fault
(ex. V8 models)
34 O, R, C (Trucks ONLY): EVAP control system
fault / voltage higher than closed limit (V8
models)
34 C, O, R Defective EGR pressure transducer sensor
35 R (Cars ONLY): RPM too low for EGR test
(2.3L MAP)
35 O, R, C (Cars ONLY): EVP/PFE voltage high
35 O, R, C (Trucks ONLY): No EGE position signal,
RPM low
35 O, R, C (Trucks ONLY): EVAP control system fault
(V8 models)
36 R System indicates lean at idle
36 R Insufficient RPM increase during speed
control test
37 R System indicates rich at idle
37 R Insufficient RPM increase during speed
control test
38 C DC motor idle speed control / idle tracking
throttle position sensor open circuit
39 C (Cars ONLY): Automatic overdrive not
operating properly (transmission failure)
41 R HEGO (HO2S) sensor voltage low / system
lean
41 C HEGO (HO2S) sensor signal out of range /
always lean
41 C No HO2S switching detected
42 R HEGO (HO2S) sensor voltage high / system
rich
42 C (Cars ONLY): HEGO (HO2S) sensor signal
out of range / always rich

49 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (42 - 55)

TEST
CODE CONDITION FAULT CODE DEFINITION
42 C No O2S switching detected
43 C (Cars ONLY): Lean HEGO (HO2S) at wide
open throttle
43 R, C (Trucks ONLY): Throttle position sensor
below idle spec (Diesel)
44 R Thermactor air system fault
45 R Thermactor air upstream
45 C DIS coil pack circuit failure
46 R Thermactor air is not bypassed
46 C (Cars ONLY): DIS coil pack circuit failure
47 O 4 x 4 switch closed (E4OD)
47 R (Cars ONLY): Vane air flow low at idle
47 C Spark timing error
48 R (Cars ONLY): Vane Air flow high at idle
48 C (Cars ONLY): DIS coil pack circuit failure
/ left side
48 C Loss of ignition diagnostic monitor LH side
48 C Coil #3 circuit failure
49 C (Cars ONLY): SPOUT signal problem
49 C (Trucks ONLY): 1-2 shift error
51 O, C ECT sensor out of range indicated / circuit
open
52 O (Cars ONLY): PSPS (PSP) circuit open
52 R (Cars ONLY): PSPS (PSP) circuit out of
range
52 O, R (Trucks ONLY): Power steering pressure
switch open
53 O, C Throttle Position sensor above maximum
voltage
53 C, O Fuel injector pump lever sensor input is
greater than self test
54 O, C Intake Air charge temperature sensor
circuit open; vane air flow sensor out of
range
55 R (Cars ONLY): Open connection in ignition
key circuit

Chapter 4 50
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (55 - 62) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
55 R (Trucks ONLY): Charging system fault
56 O, C (Cars ONLY): Mass or vane air flow sensor
above maximum voltage transmission
sensor failure
56 C (Trucks ONLY): Mass Air Flow sensor
fault (voltage higher than normal) (4.0L
models)
56 O, C (Trucks ONLY): Transmission oil
temperature sensor fault (ex. 4.0L models)
57 O (Cars ONLY): Octane adjust circuit
grounded
57 C (Cars ONLY): AXOD Neutral Pressure
Switch (NPS) circuit fault; circuit open
58 O, C (Cars ONLY): Vane air control circuit
fault; circuit open
58 R (Trucks ONLY): Idle tracking switch
circuit fault
59 O (Cars ONLY): AXOD 4/3 pressure switch
circuit failure or idle adjust circuit
grounded (2.9L MAP)
59 O, C (Cars ONLY): AXOD 4/3 pressure switch
circuit failure or 2-3 shift error (E4OD)
59 O, C (Cars ONLY): Low speed fuel pump circuit
failure
59 C (Trucks ONLY): Transmission throttle
pressure switch circuit fault (1985 through
1988 models)
59 C (Trucks ONLY): 2-3 shift error (1989
models)
61 O, C Engine coolant temperature sensor fault or
circuit grounded
62 O (Cars ONLY): AXOD 4/3 or 3/2 pressure
switch circuit failure; circuit closed
62 C (Cars ONLY): Transmission clutch fault
(E4OD)
62 O, R (Trucks ONLY): Transmission 4/3 circuit
fault

51 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (63 - 68)

TEST
CODE CONDITION FAULT CODE DEFINITION
63 O, C Throttle Position (TP) circuit fault, below
minimum voltage
63 C, O Fuel injection pump lever sensor input is
less than self test minimum (Diesel)
64 O, C ACT (IAT)/vane air temperature sensor
fault or circuit grounded
65 R Overdrive Cancel Switch not changing
state (E40D); transmission fault
65 R (Trucks ONLY): Charging system (1985
through 1988 models)
65 C (Cars ONLY): Fuel injector never went
closed loop
66 R, C (Cars ONLY): VAF/mass air flow sensor
fault, below minimum voltage
66 C (Trucks ONLY): MAF circuit below voltage
(4.0L models)
66 O, C TOT sensor signal input below self-test
minimum, or vane air flow circuit below
minimum (E4OD)
67 O Neutral Pressure Switch (NPS) circuit
failure, circuit open (3.0L MAP, 3.0L MAF-
SFI, 3.8L SFI)
67 C (Cars ONLY): Clutch switch circuit failure
67 C (Trucks ONLY): Air conditioning
compressor clutch switch fault
67 O, R (Cars ONLY): Neutral Drive Switch (NDS)
circuit failure, circuit open; or A/C input
high
67 O, C (Cars ONLY): Manual Lever Position
(MLP) sensor out of range; or A/C input
high (4.9L MAP, 5.8L MAP)
68 O, C (Cars ONLY): Vane air temperature circuit
grounded
68 O, R, C (Cars ONLY): Transmission temperature
switch circuit failure; circuit open
68 C (Trucks ONLY): Transmission oil
temperature over heat

Chapter 4 52
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (68 - 79) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
68 O (Trucks ONLY): Idle tracking switch (1985
through 1989 models)
69 O (Cars ONLY): AXOD 4/3 or 3/2 pressure
switch circuit failure; circuit closed
69 O (Trucks ONLY): Vehicle Speed Sensor fault
69 C AXOD 4/3 or 3/2 pressure switch circuit
failure, circuit open; or 3-4 shift error
(E4OD)
70 C (Cars ONLY): ECM failure
71 C (Cars ONLY): ECM reinitialization
detected on Cluster Control Assembly
(CCA) circuit failure
71 C Idle tracking switch closed on pre-position
72 C (Cars ONLY): System power circuit fault;
Message Center Control Assembly (MCCA)
circuit failure
72 R MAP, MAF or BP sensor out of range
during Dynamic Response Test
73 O (Cars ONLY): Insufficient throttle position
change
73 R (Cars ONLY): Throttle Position Sensor
fault / insufficient range
73 O, R (Trucks ONLY): Insufficient Throttle
Position change during Dynamic Response
Test
74 R Brake On/Off (BOO) switch fault; not
actuated
75 R Brake On/Off (BOO) switch fault / closed
circuit
76 R (Cars ONLY): Vane air flow sensor fault /
insufficient range during Dynamic
Response Test
77 R Operator error during Dynamic Response
Test / Wide Open Throttle not sensed
78 C (Trucks ONLY): Time delay relay fault
79 O (Cars ONLY): Air Conditioner "ON" during
Self-Test / defrost on

53 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (79 - 89)

TEST
CODE CONDITION FAULT CODE DEFINITION
79 - (Trucks ONLY): Air conditioner on while
performing test
81 O Air diverter solenoid fault, intake air
control circuit fault / air injection diverter
82 O Air diverter solenoid circuit fault or
supercharger bypass circuit fault
82 O Integrated relay control module
83 O EGR solenoid circuit fault (2.3L MAP)
83 O (Cars ONLY): Cooling fan circuit fault
83 O, C (Cars ONLY): Low speed fuel pump relay
circuit fault, circuit open (3.0L MAF-SFI)
83 O EVP/EGRC/EGRV
84 O, R (Cars ONLY): EGR vacuum regulator
circuit failure
84 O (Trucks ONLY): EGR vent fault
85 O, R (Cars ONLY): Canister Purge Solenoid
circuit failure
85 C (Cars ONLY): Adaptive fuel limit reached -
lean
85 O (Trucks ONLY): Canister purge circuit
failure
85 O Shift solenoid 3/4 - 4/3
86 O Adaptive fuel limit reached or 3-4 shift
solenoid circuit failure
86 C (Cars ONLY): Adaptive fuel limit reached -
rich
87 O, R, C (Cars ONLY): Fuel pump primary circuit
fault
87 O (Trucks ONLY): Primary fuel pump circuit
failure
88 O (Cars ONLY): Cooling fan circuit fault
88 O (Trucks ONLY): Choke relay out of range
88 C Dual plug input control failure
88 O Shift solenoid 3/4 - 4/3
89 O AXOD Lock-Up Solenoid (LUS) circuit
failure or Clutch Converter Override (CCO)
circuit failure

Chapter 4 54
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (89 - 112) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
89 O Exhaust heat control
91 O Shift Solenoid 1 (SS1) circuit failure
91 R (Cars ONLY): HEGO (HO2S) sensor
voltage low / system lean
91 C (Cars ONLY): HEGO (HO2S) sensor signal
out of range /always lean
92 O Shift Solenoid 2 (SS2) circuit failure
92 R (Cars ONLY): HEGO (HO2S) sensor
voltage high / system rich
93 O (Cars ONLY): Throttle position sensor
signal input low at maximum DC motor
extension or Converter Clutch Control
(CCC) circuit failure
93 O (Trucks ONLY): Coast clutch circuit failure
94 O Converter Clutch Control (CCC) circuit
failure
94 R (Cars ONLY): Air diverter solenoid circuit
fault
95 O, C Fuel pump secondary circuit fault
96 O, C Fuel pump secondary circuit fault / high
speed fuel pump relay open
97 O Overdrive Cancel Indicator Light (OCIL)
circuit failure
98 O Electronic Pressure Control (EPC) driver
failure in processor
98 R (Cars ONLY): Hard fault is present -
FMEM mode
98 R (Trucks ONLY): Test failure, hard fault
repeat sequence (1985 through 1988)
99 O, C Electronic Pressure Control (EPC) circuit
failure
99 R (Cars ONLY): EEC system has not learned
to control idle
111 O, R, C System PASS
112 O, C (Cars ONLY): Intake Air Temperature
(IAT) sensor circuit below minimum voltage
/ 254°F indicated

55 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (112 - 138)

TEST
CODE CONDITION FAULT CODE DEFINITION
112 O, C (Trucks ONLY): Air charge temperature
sensor below minimum voltage
113 O, C Intake air charge temperature sensor above
maximum voltage / -40° indicated
114 O, R Air charge temperature sensor higher or
lower than expected voltage
116 O, R Engine coolant temperature higher or lower
than expected
117 O, C Engine coolant temperature sensor below
minimum voltage / 254° F indicated
118 O, C Engine coolant temperature sensor above
maximum voltage / 0 to -40° F indicated
121 O, R, C Closed throttle voltage higher or lower than
expected
122 O, C Throttle Position sensor below minimum
voltage
123 O, C Throttle Position sensor above maximum
voltage
124 C Throttle Position sensor voltage above
normal
125 C Throttle Position sensor voltage below
normal
126 O, R, C Manifold absolute pressure (MAP) or
barometric sensor (BARO) above or below
normal
126 C Cylinder identification circuit failure
128 R (Cars ONLY): Manifold absolute pressure
sensor failure/ vacuum hose disconnected or
damaged
128 C (Trucks ONLY): Manifold absolute
pressure sensor / vacuum hose disconnected
or damaged
129 R Insufficient Mass Air Flow (MAF) change
during dynamic response test
136 R HEGO (HO2S) sensor fault, always lean
137 R HEGO (HO2S) sensor fault, always rich
138 R Cold start injector flow insufficient

Chapter 4 56
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (139 - 181) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
139 C (Cars ONLY): HEGO (HO2S) sensor switch
fault
141 R Flexible fuel control / fuel system lean
144 C HEGO (HO2S) sensor switch fault
157 C Mass Air Flow sensor fault, low voltage
158 O, C Mass Air Flow sensor fault, high voltage
159 O, R Mass Air Flow sensor fault, above or below
normal
167 R Throttle Position sensor fault during
dynamic response test
171 C (Cars ONLY): HEGO (HO2S) sensor
fault/not switching, or fuel system at
adaptive limits
171 C (Trucks ONLY): HEGO (HO2S) sensor
fault/not switching
172 R, C HEGO (HO2S) sensor fault/lean
173 R, C HEGO (HO2S) sensor fault/rich
174 C (Cars ONLY): HEGO switching time slow
175 C (Cars ONLY): HEGO (HO2S) sensor
fault/not switching, or fuel system at
adaptive limits
175 C (Trucks ONLY): HEGO (HO2S) sensor
fault/not switching
176 C HEGO (HO2S) sensor fault/always lean
176 R* Insufficient TP change during no oxygen
sensor switch detected
177 C HEGO (HO2S) sensor fault/always rich
177 * No oxygen sensor switch detected
178 C (Cars ONLY): HEGO switching time slow
179 C (Cars ONLY): Fuel system at lean adaptive
limit at partial throttle / system rich
179 C (Trucks ONLY): HEGO (HO2S) sensor
fault unable to switch / rich during part
throttle
181 C (Cars ONLY): Fuel system at rich adaptive
limit at partial throttle / system lean

57 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (181 - 216)

TEST
CODE CONDITION FAULT CODE DEFINITION
181 C (Trucks ONLY): HEGO (HO2S) sensor
fault unable to switch / lean during part
throttle
182 C Fuel system at lean adaptive limit at idle /
system rich
183 C Fuel system at rich adaptive limit at idle /
system lean
184 C Mass Air Flow sensor above normal
185 C Mass Air Flow sensor below normal
186 C Fault in injector pulse width circuit / high
187 C Fault in injector pulse width circuit / low
188 C (Cars ONLY): Fuel system at lean adaptive
limit at partial throttle / system rich
188 C (Trucks ONLY): HEGO (HO2S) sensor
fault unable to switch / rich during part
throttle
189 C (Cars ONLY): Fuel system at rich adaptive
limit at partial throttle / system lean
189 C (Trucks ONLY): HEGO (HO2S) sensor
fault unable to switch / lean during part
throttle
190 * Adaptive fuel lean limit reached at “Idle,
system rich”
191 C (Cars ONLY): Fuel system at lean adaptive
limit at idle / system rich
192 C (Cars ONLY): Fuel system at rich adaptive
limit at idle / system lean
193 O (Cars ONLY): Flexible fuel sensor circuit
fault
211 C Profile Ignition Pickup (PIP) circuit fault
212 C Loss of ignition diagnostic monitor
signal/SPOUT circuit grounded
213 R SPOUT circuit open
214 C Cylinder identification circuit failure
215 C DIS fault ignition system - coil #1
216 C DIS fault ignition system - coil #2

Chapter 4 58
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (217 - 311) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
217 C DIS fault ignition system - coil #3
218 C Loss of Ignition Diagnostic Monitor (IDM)
signal/left side
219 C (Cars ONLY): SPOUT signal defaulted to
10° BTDC / SPOUT circuit open
221 C Spark timing error
222 C Distributorless Ignition System - loss of
right side ignition Diagnostic Monitor
(IDM) signal
223 C Distributorless Ignition System - loss of
dual plug inhibit (DPI) control
224 C Erratic IDM input to processor
224 C (Trucks ONLY): SPOUT circuit ground/coil
1, 2, 3 or 4
225 R Knock sensor fault during dynamic
response test
226 C (Cars ONLY): Ignition diagnostic Monitor
(IDM) signal not received
226 C (Trucks ONLY): Electronic Distributorless
Ignition System (EDIS) problem -
Crankshaft Position Sensor (CPS) problem
227 * Crank position sensor
232 C (Trucks ONLY): Electronic Distributorless
Ignition System (EDIS) Coil 1, 2, 3 or 4
circuit fault
233 * Spark angel pulse width error
238 C PCM detect coil 4 primary circuit failure
239 * Crank position signal received with engine
off
241 * EDIS to EEC processor ignition diagnostic
module pulse width transmission error
242 * Operating in DIS failure mode
243 * Secondary circuit failure
244 R Cylinder identification circuit failure
311 R Thermactor air system/fault during engine
run self-test

59 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (312 - 416)

TEST
CODE CONDITION FAULT CODE DEFINITION
312 R Thermactor air system/fault during engine
run self-test
313 R Thermactor air system/air not bypassed
during self-test
314 R (Cars ONLY): Thermactor air system/fault
during engine run self-test / left side
326 R, C (Cars ONLY): EGR sensor circuit voltage
lower than expected
327 O, R, C EGR valve position circuit below minimum
voltage
327 * EVP/EPT circuit below minimum voltage
328 O, R, C EGR closed valve voltage lower than
expected
332 R, C Insufficient EGR flow detected
334 O, R, C EGR closed valve voltage high
335 O EGR sensor circuit voltage higher or lower
than expected during self-test
336 R, C EGR sensor circuit voltage higher than
expected
336 R, C (Trucks ONLY): Exhaust pressure high
337 O, R, C EGR sensor circuit above maximum voltage
338 C (Cars ONLY): Engine Coolant temperature
(ECT) lower than expected
339 C (Cars ONLY): Engine Coolant temperature
(ECT) higher than expected
341 R (Cars ONLY): Octane adjust service pin
open
381 C Erratic A/C compressor clutch cycling
411 R Cannot control RPM during KOER low
RPM check
412 R Cannot control RPM during KOER high
RPM check
415 * Idle speed control system at minimum
learning limit
416 * Idle air control system at maximum
learning limit

Chapter 4 60
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (452 - 533) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
452 R (Cars ONLY): Vehicle Speed Sensor (VSS)
signal fault
452 C (Trucks ONLY): Vehicle Speed Sensor
(VSS) signal fault
453 * Servo leaking down during test
454 * Servo leaking up during test
455 * Insufficient RPM increase during speed
456 * Insufficient RPM decrease during test
457 * Speed control command switches circuit
not functioning
458 * Speed control command switches stuck or
circuit control
459 * Speed control ground circuit open
511 O Read Only Memory (ROM) test failure
512 C Keep Alive Memory (KAM) test failure
513 C PCM internal voltage failure
519 O Power Steering Pressure Switch circuit
open
521 R Power Steering Pressure Switch circuit
fault
522 O Vehicle not in Park or Neutral during
KOEO
524 O, C (Cars ONLY): Low speed fuel pump circuit
open - battery to ECA
525 O (Cars ONLY): Vehicle was in gear or A/C
on during self-test
526 O (Cars ONLY): Neutral Pressure Switch
NPS (PNP) circuit closed; A/C on
527 O (Cars ONLY): Neutral Drive Switch NDS
(PNP) circuit open; A/C on
528 C Clutch switch circuit fault
529 C (Cars ONLY): Data communications link
or EEC circuit fault
532 * Cluster control assembly circuit failure
533 C (Cars ONLY): Data communications link
or EIC circuit fault

61 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (536 - 568)

TEST
CODE CONDITION FAULT CODE DEFINITION
536 R, C Brake On/Off (BOO) circuit not activated
during KOER
538 R Insufficient RPM change during KOER
Dynamic Response Test/
538 R (Trucks ONLY): invalid cylinder balance
test due to throttle movement during test
539 O A/C on/Defrost on during KOEO
542 O, C Fuel pump secondary circuit fault
543 O, C Fuel pump secondary circuit fault
551 O Idle Air Control solenoid circuit fault
552 O Thermactor air bypass solenoid circuit fault
552 * Air management circuit 1 failure
553 O Thermactor air diverter solenoid circuit
fault
553 * Air management circuit 2 failure
554 O (Cars ONLY): Fuel Pressure Regulator
Control (FPRC) circuit failure
554 * Fuel pressure regulator control circuit
failure
555 * Supercharger bypass solenoid circuit
failure
556 O, C Fuel pump relay primary circuit fault
557 O, C Fuel pump primary circuit failure
558 O EGR valve regulator solenoid circuit fault
559 O (Cars ONLY): Air conditioning ON relay
circuit failure
562 * Auxiliary electric fan circuit failure
563 O (Cars ONLY): High Speed Electro Drive
Fan circuit fault
564 O (Cars ONLY): Electro Drive Fan circuit
fault
565 O Canister purge solenoid circuit fault
566 O 3-4 shift solenoid circuit failure
567 * Speed control vent circuit failure
568 * Speed control vacuum circuit failure

Chapter 4 62
Retrieving Codes
FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (569 - 631) 4
TEST
CODE CONDITION FAULT CODE DEFINITION
569 O (Trucks ONLY): Auxiliary Canister Purge
(AUX-CANP) circuit failure
571 O EGR circuit failure
572 O EGR circuit failure
578 C A/C pressure sensor circuit
579 C Insufficient A/C pressure change
581 C Power to fan circuit over current
582 O Fan circuit open
583 C Power to fuel pump over current
584 C Power ground circuit open
585 C Power to A/C clutch over current
586 C A/C clutch circuit open
587 C, O Vehicle control relay module
communication failure
617 C Transmission problem (1-2 shift error)
618 C Transmission problem (2-3 shift error)
619 C Transmission problem (3-4 shift error)
621 O Shift Solenoid #1 circuit fault
622 O Shift Solenoid #2 circuit fault
623 C, O Transmission control indicator lamp
circuit failure
624 O, C Electronic Pressure Control solenoid circuit
fault
625 O Electronic Pressure Control solenoid circuit
fault
625 C, O, R Hard fault is present
626 O Coast Clutch solenoid circuit fault
627 O, C Converter Clutch Control solenoid circuit
fault
628 O, C Excessive converter clutch slippage
628 O (Cars ONLY): Lock-up solenoid failure
629 O Converter clutch solenoid circuit fault or
lock-up solenoid circuit fault
631 O Overdrive Transmission Cancel Indicator
Light circuit fault

63 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITIONS FOR EEC-IV SYSTEMS (632 - 655)

TEST
CODE CONDITION FAULT CODE DEFINITION
632 R Overdrive Transmission Cancel Switch/ no
action during self engine run test
633 O 4 x 4 switch is closed
634 C Manual Lever Position sensor voltage
higher or lower than expected or A/C on
636 O, R Transmission Oil Temperature higher or
lower than expected
637 O, C Transmission Oil Temperature circuit
above maximum voltage
638 O, C Transmission Oil Temperature circuit
below minimum voltage
639 R, C Insufficient input from transmission speed
sensor
641 O (Cars ONLY): Shift Solenoid #3 circuit
fault
643 O, C (Cars ONLY): Converter Clutch Control
(CCC) circuit failure
645 C (Cars ONLY): Incorrect gear ratio-first
gear
646 C (Cars ONLY): Incorrect gear ratio-second
gear
647 C (Cars ONLY): Incorrect gear ratio-third
gear
648 C (Cars ONLY): Incorrect gear ratio-fourth
gear
649 C (Cars ONLY): Electronic Pressure Control
Circuit solenoid higher or lower than
expected
651 C (Cars ONLY): Electronic Pressure Control
circuit solenoid failure
652 O (Cars ONLY): Modulated Lock-Up Torque
Converter Clutch Solenoid circuit fault
652 C Transmission over temp condition
654 O Not in "park" during KOEO Self-test
655 C (Trucks ONLY): Manual Lever Position
(MLP) sensor indicating not in NEUTRAL
during Self-Test

Chapter 4 64
Retrieving Codes
RETRIEVING FAULT CODES FROM MCU SYSTEMS 4
TEST
CODE CONDITION FAULT CODE DEFINITION
656 C Converter Clutch Control (CCC) continuous
slip error
659 R High vehicle speed in park indication
662 O Shift solenoid 2 circuit
667 C, O Transmission range sensor circuit below
maximum voltage
668 C, O Transmission range sensor circuit above
maximum voltage
675 O, R Transmission range sensor circuit voltage
out of range
675 C Cluster center control circuit failed
dynamic response test
998 R Operating in failure mode
NO CODES Unable to initiate Self-Test or unable to
output Self-Test codes

* Test condition not available

RETRIEVING FAULT CODES FROM MCU SYSTEMS

Preliminary Procedures
The following "Preliminary Procedures" MUST be
performed before the actual KOEO and/or KOER Self
Tests are performed.
• Always observe safety precautions before and during
testing process.

• Fix any known mechanical problem before this test.

• A voltmeter is required to perform this test.

1. Idle engine until it reaches normal operating temperature.
2. While engine is running, use a voltmeter to check voltages
between the choke cap and engine ground. For battery
powered choke, voltage should be approximately 12 volts.
For alternator powered choke, voltage should be
approximately 7.5 volts.
3. Turn ignition off.
4. If your vehicle has one or more of the following
configurations perform the Set-Up Procedures as
described below:

65 Chapter 4
 Retrieving Codes
4 KOEO SELF TEST (MCU SYSTEMS)

■ In-Line 4 and In-Line 6 with canister control

valve: Remove hose from connector port B. Reconnect
after testing is completed.
■ V-6 and V-8: Remove PCV valve: Reconnect after
testing is completed.
■ 2.3L with GK code: Locate the anti-backfire vacuum
switch tee behind the MCU module and remove the
cap. Reconnect after testing is completed.
■ 2.3L with EGR vacuum load control valve: Cover
vacuum valve vent holes with tape. Remove the tape
after testing is completed.
■ 4.2L with vacuum delay valve: Uncap restrictor in
Thermactor Air Diverter (TAD) solenoid vacuum line.
Reconnect after testing is completed.
■ 5.8L with vacuum delay valve: Uncap restrictor in
Thermactor Air Bypass (TAB) solenoid vacuum line.
Reconnect after testing is completed.

KEY ON ENGINE OFF (KOEO) SELF TEST (MCU

SYSTEMS)

• The "Preliminary Procedures" (page 66) must be

completed before performing the KOEO Self Test

• Always observe safety precautions before and during

testing process.

• ALWAYS check Code Reader battery before retrieving

fault codes.

• Fix any known mechanical problems before this test.

1. Warm-up engine to normal operating temperature before
this test.
2. Turn ignition off.
3. Turn the Code Reader switch to OFF then connect it to
the vehicle's test connector.
■ MCU Systems have one six pin connector only.

Chapter 4 66
Retrieving Codes
KOEO SELF TEST (MCU SYSTEMS) 4
4. Press and release the ON/OFF
button to turn the Code Reader
"ON".
■ Three zeros should be visible
on the display at this time.
5. Press and release the TEST/HOLD Button to put the code
reader in TEST mode.
6. Turn on ignition. DO NOT START THE ENGINE.
■ The display will show a
"Triangle" Icon on the lower
right hand corner of the
screen to indicate that the
code reader is in test mode.
7. After about 4 to 30 seconds (it may take longer on some
vehicles) the computer will start sending the test results
to the Code Reader in the form of numerical codes.
■ A square icon on the right
hand side of the screen will
appear and flash each time O

the Code Reader receives a

code, and then the code will
be displayed on the Code
Reader's screen.
■ A small "O" will be visible in the upper right hand
corner of the screen to indicate that the code being
received is a KOEO Self Test fault code.
8. After all the KOEO Self Test codes are received (wait until
the flashing square icon no longer appears on the screen
for 30 consecutive seconds to ensure that all the codes
have been retrieved), turn the Code Reader off.
■ The codes retrieved are now stored in the Code
Reader's memory.
9. Turn the ignition off and disconnect the Code Reader from
the vehicle's test connector. The codes retrieved are now
stored in the Code Reader's memory.
10. To view codes stored in the Code Reader's memory, press
the ON/OFF button to turn the Code Reader on, then
press and release the MEMORY button; the first stored
code will display. Continue pressing and releasing the
MEMORY button to scroll through the stored codes until
all the codes have been displayed.

67 Chapter 4
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4 KOER SELF TEST (MCU SYSTEMS)

NOTE: All retrieved codes will stay in the Code Reader's

memory and will only clear from the Code Reader's
memory if the Self Test procedure is performed again
(codes from a prior test will clear automatically when new
Self Test is performed) or if batteries are removed from the
Code Reader.
11. Go to page 72 for "FAULT CODE DEFINITION FOR
MCU SYSTEMS". Use the code definitions as a guide and
follow the manufacturer's service procedures in the
vehicle's service manual to troubleshoot and repair faults.
■ All KOEO Self Test codes that are received by the
Code Reader during the KOEO Self Test represent
problems that are present now (at the time the test is
performed). The related vehicle problems that cause
these codes to set must be repaired using the
procedures described in the vehicle's service manual.
12. After all repairs have been completed, repeat the KOEO
Self Test to verify the repair was successful. Do not
proceed to the KOER Self test until all the problems that
caused any KOEO fault codes to set are repaired.

KEY ON ENGINE RUNNING (KOER) SELF TEST (MCU

SYSTEMS)
IMPORTANT: The "Preliminary Procedures" (page 66) and
the "KOEO Self Test" (page 67) must be completed first, before
the KOER Self-Test is performed; otherwise test results might
be invalid.
When the KOER Self Test is activated, it tests the operation of
the actuators, relays, switches, etc. under actual engine
operating conditions. During this test, the computer sends
electrical signals to some of these devices and waits for their
response to see if its commands are carried out properly.
If the response from any of these devices is incorrect, that
particular device fails the test and the computer assigns a
numerical Fault Code that is specific to the device, circuit
and/or system where the problem was detected. All faults
detected during the KOER Self Test are sent to the Code
Reader as numerical fault codes for further evaluation.
• Always observe all safety precautions before and during
the testing process.

• ALWAYS check the Code Reader's batteries before

conducting the test.

Chapter 4 68
Retrieving Codes
KOER SELF TEST (MCU SYSTEMS) 4
NOTE: For vehicles with 2.3L HSC (High Swirl Combustion)
engines: Locate vacuum tee and restrictor in the thermactor
vacuum control line, and uncap during KOER Test Reconnect
after testing is completed.
1. Turn ignition off.
2. Press the ON/OFF Button to turn Code Reader OFF, then
connect the Code Reader to the vehicle's test connector.
■ MCU systems are equipped with only one 6-pin
connector (see page 18 for details).
3. Turn Code Reader ON, then
press and release TEST/HOLD
button to place the Code Reader
in TEST mode.
■ Three zeros should be visible
on the display at this time.
4. Start the engine.
■ For In-Line 4 And In-Line 6 engines, do the
following:
Gradually increase engine speed to 3,000 RPM and
hold this speed until codes appear on the Code
Reader's display.
When codes begin to appear on the Code Reader's
display, return engine speed to idle. Proceed to step 5.
■ For V-6 or V-8 engines, do the following:
Gradually increase engine speed to 2,500 RPM and
hold for 2 minutes, then reduce engine speed back to
idle.
Turn off engine. Restart engine and let idle. Proceed
to step 5.
5. Read diagnostic trouble codes on the Code Reader's display.
■ A square icon on the right
hand side of the screen will
CYL R
appear and flash each time
the Code Reader receives a
code, and then the code will
be displayed on the Code
Reader's screen.

69 Chapter 4
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4 KOER SELF TEST (MCU SYSTEMS)

■ The first code displayed by the Code Reader is the

Cylinder Identification (ID) Code. The cylinder ID
code identifies the number of cylinders of the vehicle
that is under test.
■ A small "R" will show in the upper right hand corner
of the display to indicate that the code being retrieved
is a Key On Engine Running (KOER) code.
NOTE: If all the procedures are followed and the Code
Reader fails to work, refer to "Troubleshooting" on
page 75.
6. Test the knock sensor (if applicable) after the cylinder ID
code is transmitted. Place a steel shaft near the bottom of
the knock sensor (not on the sensor). With a light
hammer, knock slowly on the end of the shaft for 15
seconds.
NOTE: For vehicles equipped with knock sensors:
Code 25 may display if the knock sensor test in step 6
is not performed.
7. If any problems are detected on any components or
circuits as they are being tested, a numerical code
(Diagnostic Trouble Code) will be sent to the Code Reader.
8. After all the KOER Self Test Codes are received by the
Code Reader (wait until the flashing square icon no longer
appears on the screen for 30 consecutive seconds to ensure
that all the codes have been retrieved), turn the Code
Reader off.
9. Turn the engine off and disconnect the Code Reader from
the vehicle's test connector. The codes received are now
stored in the Code Reader's memory.
10. To view codes stored in the Code Reader's memory, press
the ON/OFF button to turn the Code Reader on, then
press and release the MEMORY button; the first stored
code will display. Continue pressing and releasing the
MEMORY button to scroll through the stored codes until
all the codes have been displayed.
NOTE: All retrieved codes will stay in the Code Reader's
memory and will only clear from the Code Reader's
memory if the Self Test procedure is performed again
(codes from a prior test will clear automatically when new
Self Test is performed) or if batteries are removed from the
Code Reader.

Chapter 4 70
Retrieving Codes
FAULT CODE DEFINITIONS FOR MCU SYSTEMS (11 - 45) 4
■ Refer to page 72 for "Fault Code Definitions for MCU
Systems". Use the code definition as a guide and
follow the manufacturer's service procedures in the
vehicle's service repair manual to troubleshoot and
repair faults.
■ All KOER codes that are received by the Code Reader
during the KOER Self test represent problems that
are present now (at the time the test is performed).
The related vehicle problems that cause these codes to
set must be repaired using the procedures described
in the vehicle's repair manual.
11. After all repairs have been completed, repeat the KOER
Self Test to confirm the repair was successful.

FAULT CODE DEFINITION FOR MCU SYSTEMS CAR &

TRUCK

CODE FAULT CODE DEFINITION

11 NOTE: "High Altitude" refers to vehicles computer
adjusted for high elevations.
I-4 (All except High Altitude): System OK
I-4 (High Altitude only): Altitude (ALT) circuit is open.
I-6: System OK.
V-6 (All except High Altitude): System OK.
V-6 (High Altitude only): Altitude (ALT) circuit is open.
V-8 (All except High Altitude): System OK.
V-8 (High Altitude only): Altitude (ALT) circuit is open.
12 V-8: RPM out of range (throttle kicker).
25 V-8: Knock Sensor (KS) signal not detected.
33 I-4, I-6, V-6: Key On Engine Running (KOER) Self-Test
not initiated.
41 All Engines: Exhaust Gas Oxygen sensor: voltage signal
lean (low).
42 All Engines: Exhaust Gas Oxygen sensor: voltage signal
rich (high).
44 All Engines: Oxygen sensor signal indicates Rich -
excessive fuel, restricted air intake — or — Inoperative
Thermactor System
45 All Engines: Thermactor air flow going upstream to
exhaust manifold.

71 Chapter 4
 Retrieving Codes
4 FAULT CODE DEFINITION FOR MCU SYSTEMS (46 - 64)

CODE FAULT CODE DEFINITION

46 All Engines: Thermactor Air System unable to bypass.
51 I-4: Low or Mid Temperature Switch is open when
engine is hot.
I-6: Low or Mid Temperature Vacuum Switch is open
when engine is hot.
V-6: Hi or Hi/Low Vacuum Switch is always open.
V-8: Hi or Hi/Low Vacuum Switch is always open.
52 I-4 (car): Idle Tracking Switch (ITS) - voltage does not
change from closed to open throttle.
I-4 (truck): Idle/Decel Vacuum Switch open constantly.
I-6: Wide Open Throttle Vacuum Switch is open
constantly.
53 I-4: Wide Open Throttle Vacuum Switch open constantly.
I-6: CROWD Vacuum Switch open constantly.
V-6: Dual Temperature Switch is open constantly.
V-8: Dual Temperature Switch is open constantly.
54 V-8: Mid Temperature Switch is open constantly.
55 V-8: Mid Vacuum Switch is open constantly.
56 I-6: Closed Throttle Vacuum Switch is open constantly.
61 V-8: Hi/Low Vacuum Switch is closed constantly.
62 NOTE: "High Altitude" refers to vehicles computer
adjusted for operation at high elevations.
I-4 (car): Idle Tracking Switch is closed at idle.
I-4 (truck): Idle/Decel Vacuum Switch is closed constantly.
I-6: Wide Open Throttle Vacuum Switch is closed
constantly.
V-6 (All except High Altitude): Altitude circuit is open.
V-6 (High Altitude only): System OK.
V-8 (All except High Altitude): Altitude (ALT) circuit is
open.
V-8 (High Altitude only): System OK.
63 I-4: Wide Open Throttle Vacuum Switch is closed
constantly.
I-6: CROWD Vacuum Switch is closed constantly.
64 NOTE: "High Altitude" refers to vehicles that are
computer adjusted for high elevation operation.
I-4: (All except High Altitude): Altitude circuit is open.
I-4: (High Altitude only): System OK.
V-6: Mid Vacuum Switch is closed constantly.
V-8: Mid Vacuum Switch is closed constantly.

Chapter 4 72
Retrieving Codes
FAULT CODE DEFINITION FOR MCU SYSTEMS (65 - 66) 4
CODE FAULT CODE DEFINITION
65 NOTE: "High Altitude" refers to vehicles that are
computer adjusted for high elevation operation.
I-4: (All except High Altitude): Altitude circuit is open.
I-4: (High Altitude Only): System OK.
V-6: Mid Vacuum Switch is closed constantly.
V-8: Mid Vacuum Switch is closed constantly.
66 I-6: Closed Throttle Vacuum Switch is closed constantly.

73 Chapter 4
 Retrieving Codes
4

Chapter 4 74
Troubleshooting
CODE READER TROUBLESHOOTING GUIDE 5
CODE READER TROUBLESHOOTING GUIDE
If all procedures are followed and the Code Reader will not
retrieve codes when performing the Key On Engine Off
(KOEO) Self Test, check the following:
1. Code Reader's batteries, change batteries as required.
2. Check the vehicles Test Connector pins for corrosion and
clean as necessary.
NOTE: The Code Reader receives a ground signal from one of
the pins of the vehicle's Test Connectors and uses it to signal
the computer to initiate the Self-Tests. A problem in the
vehicle's Test Connector ground pin or circuit will result in an
improper ground being supplied to the code reader which will
effect the code reader's ability to signal the computer to initiate
the Self Test. If after performing the procedures in step one and
two, the code reader still does not work proceed to EEC-IV
Systems/ MCU Systems bellow (as applicable).

EEC-IV Systems (most 1985-95 vehicles)

On some vehicles equipped with the EEC-IV Computer
Systems the vehicle's Test Connector ground circuit may have
a poor ground due to bad ground point connections, old and
corroded wiring, poor connector to wire contacts etc. that will
prevent the Code Reader from initiating the Self-Test. To
alleviate this problem and allow the Code Reader to initiate
the Self-Test, perform the following steps.
1. Disconnect the single pin
Vehicle's Test Connector from
the code reader (leave the six
pin Test Connector connected
to code reader).
2. Route a jumper wire from the
vehicle's harness single pin
Test Connector to the + - MEMORY
ON / OFF

vehicle's battery negative post TEST /

HOLD

or to a clean spot in the

vehicle's metal frame. See
drawing.
3. Proceed with KOEO Self Test as per KOEO instructions.

75 Chapter 5
 Troubleshooting
5 CODE READER TROUBLESHOOTING GUIDE

MCU Systems (Most 1981-84 vehicles)

The 6-pin MCU Test Connectors
for some vehicle models are not
equipped with a ground
terminal at position "F". This
"F"
terminal is required by the code
reader to provide a ground
signal to the vehicle's computer
to initiate the Self-Test.
If no codes are displayed during
the testing procedure, check the
Test Connector for ground JUMP TO
terminal at position "F". If no GROUND
terminal is present at position
"F", connect a jumper wire from
the open terminal on the Code Reader to the negative post of
the battery or a bare clean spot in the vehicle’s metal frame.
■ If after performing all the troubleshooting procedures the
code reader still will not work consult the vehicles service
repair manual and/or contact the service department. See
page 89 for service information.

Chapter 5 76
Glossary
INTRODUCTION 6
INTRODUCTION
The Society of Automotive Engineers has issued a Standard
(SAE J1930) for Electrical/Electronic Systems Diagnostic
Terms, Definitions, Abbreviations, and Acronyms. However, at
the present time, this Standard is not in wide use by vehicle
manufacturers.
This Glossary contains definitions for abbreviations and terms
you may find in this manual or in your vehicle service manual.
These definitions may not agree with those contained in SAE
J1930.

GLOSSARY OF TERMS AND ABBREVIATIONS

4EAT – Ford electronic automatic 4 speed transaxle.
A/C – Air Conditioning.
A4LD – Ford automatic 4 speed lock-up converter drive.
AAC – Auxiliary Air Control Valve.
ABS – Anti-Lock Brake System.
ACC – Air Conditioning Clutch compressor signal input to
computer relating status of air conditioning clutch.
ACCS – Air Conditioning Cycling Switch.
ACD – Air Conditioner Demand switch.
ACT – Air Charge Temperature sensor or signal circuit.
ACV – (Thermactor) Air Control Valve.
AIR – Secondary air injection (formerly thermactor).
AIR BPV – Thermactor Air Bypass Valve.
AM1 – Thermactor Air Management (TAB).
AM2 – Thermactor Air Management (TAD).
AMBIENT TEMPERATURE – Temperature of air
surrounding vehicle being serviced.
ANTI-BFV – Anti-Backfire Valve.
AOD – Automatic Over Drive transmission.
ATDC – After Top Dead Center.
AVOM – Analog Volt/Ohm Meter.
AXOD – Automatic Overdrive transaxle.
AXOD-E – Automatic Overdrive transaxle, electronically
controlled.
BAC – Bypass Air Control valve.
BARO – Barometric Pressure.

77 Chapter 6
 Glossary
6 GLOSSARY OF TERMS AND ABBRREVIATIONS

BASE IDLE – Idle RPM when the throttle lever rests on the
throttle stop and the Idle Speed Control is fully retracted and
disconnected.
BCM – Body Computer Module.
BOO – Brake On-Off input to the computer.
BOOST – Condition of over-pressure (above atmospheric) in
the intake manifold; caused by intake air being forced in by a
turbocharger or supercharger.
BP – Barometric Pressure sensor. Used to compensate for
altitude variations.
BPA – ByPass Air solenoid.
BTDC – Before Top Dead Center.
BVT – Back-pressure Variable Transducer.
CANISTER – A container, in an evaporative emission system,
that contains charcoal to trap fuel vapors from the fuel system.
CANISTER PURGE SOLENOID – Electrical solenoid or its
control line. Solenoid opens a valve from fuel vapor canister
line to intake manifold when energized. Controls flow of
vapors between carburetor bowl vent and carbon canister.
CANP – Canister Purge solenoid.
CATALYTIC CONVERTER – Muffler like assembly placed
in exhaust system that contains a catalyst to change
hydrocarbons and carbon monoxide into water vapor and
carbon dioxide.
CCC – Converter Clutch Control solenoid or its circuit.
CCD – Computer Controlled Dwell, used on Ford Vehicles.
CCO – Converter Clutch Override output from the computer
processor to the transmission.
CCS – Coast Clutch Solenoid or its circuit.
CENTRAL FUEL INJECTION – Computer control fuel
injection at throttle body, used on Fords, same as throttle body
injection.
CER – Cold Enrichment Rod.
CES – Clutch Engage Switch.
CFI – Central Fuel Injection.
CHECK ENGINE LIGHT – Dash panel light used either to
aid in identification and diagnosis of a system problems or to
indicate that maintenance is required.
CHECK VALVE – Valve that operates like a one-way gate.
CID – Cylinder Identification sensor or its circuit.

Chapter 6 78
Glossary
GLOSSARY OF TERMS AND ABBRREVIATIONS 6
CKT – Circuit.
CL – Closed Loop.
CLC – Converter Lock-up Clutch.
CO – Carbon Monoxide.
COC – Conventional Oxidation Catalyst.
COMPUTER TIMING –Total spark advance in degrees
before top dead center. Calculated by Ford EEC-IV processor,
based on sensor input.
CONTINUOUS SELF-TEST – Continuous test of Ford EEC-
IV system conducted whenever vehicle is in operation.
CPS – Crankshaft Position Sensor. Provides the ECU with
engine speed and crankshaft angle (position).
CTS – Coolant Temperature Sensor.
CURB IDLE – Computer controlled idle rpm.
CVR – Control Vacuum Regulator.
CWM – Cold Weather Modulator.
CYLINDER IDENTIFICATION SIGNAL (CID) – A signal
generated by crankshaft timing sensor, used to synchronize
ignition coils, due to the fact that some models use a 2 ignition
coil pack DIS system.
C3I – Computer Controlled Coil Ignition. Produces ignition
spark without aid of an ignition distributor.
DCL – Data Communications Link.
DERM – Diagnostic Energy Reserve Module and air bag (SIR)
controller.
DFS – Decel Fuel Shut-off.
DIC – Driver Information Center.
DID – Driver Information Display.
DIS – Direct Ignition System. Produces ignition spark without
aid of an ignition distributor. (Similar to C3I).
DOL – Data Output Link. Fuel calculation data from EEC-IV
processor to trip computer.
DPDIS – Dual Plug Distributorless Ignition System, used on
some Ford 2.3L engines.
DPI – Dual Plug Inhibit, used on some Ford 2.3L engines.
DUAL CATALYTIC CONVERTER – Combines 2 converters
in one shell. Controls NOx, HC and CO. Also called TWC.
DURA SPARK SYSTEM – The Ford ignition system used
with the 5.8L feedback carbureted MCU control system.

79 Chapter 6
 Glossary
6 GLOSSARY OF TERMS AND ABBRREVIATIONS

DV TW – Delay Valve, 2 Way.

DVM (10 MEG) – Digital voltmeter with a minimum of 10
million ohms resistance. Allows measurement in circuit
without affecting the circuit operation.
DWELL – Amount of time (recorded on a dwell meter in
degrees) that current passes through a closed switch.
E4OD – Ford Electronic 4 speed Overdrive transmission.
EAS – Electronic Air Switching, directs airflow to catalytic
converter or exhaust ports of the engine.
EBCM – Electronic Brake Control Module.
ECA – Electronic Control Assembly. Ford’s engine controlling
computer.
ECM – Engine Control Module properly call a Powertrain
Control Module.
ECT – Engine Coolant Temperature sensor or circuit.
ECU – Electronic Control Unit. To process input information
to trigger ignition control module.
EDF – Electro-Drive Fan relay or its circuit.
EEC-IV – Electronic Engine Control design 4. A computer
controlled system of engine control used on Ford.
EECS – Evaporative Emission Control System.
EEGR – Electronic Exhaust Gas Recirculation valve (Sonic).
EEPROM – Electronically Erasable Programmable Read Only
Memory.
EET – Electronic Exhaust Gas Recirculation Transducer.
EFC – Electronic Feedback Carburetor. Utilizes an electronic
signal, generated by an exhaust gas oxygen sensor to precisely
control air/fuel mixture ratio in the carburetor.
EFI – Electronic Fuel Injection. Computer controlled fuel
injection system. On Ford EFI uses injectors in each intake
port and CFI uses an injector in the throttle body.
EGO – Exhaust Gas Oxygen sensor.
EGR – Exhaust Gas Recirculation system is designed to allow
flow of inert exhaust gases into combustion chamber to cool
combustion and reduce nitrous oxides in exhaust.
EHC – Exhaust Heat Control vacuum solenoid or its circuit.
EIC – Electronic Instrument Cluster.
ELECTRONIC SPARK CONTROL – Used to retard spark
advance if detonation occurs.

Chapter 6 80
Glossary
GLOSSARY OF TERMS AND ABBRREVIATIONS 6
ELECTRONIC SPARK TIMING – PCM controlled timing of
the ignition spark.
EMR – Electronic Module Retard, controls spark retard.
ENGINE CONTROL MODULE – A microprocessor based
device which contains electronic circuitry to control and
monitor air/fuel and emission systems, and aid in diagnostics.
EPC – Electronic Pressure Control solenoid.
EPROM – Erasable Programmable Read Only Memory.
ER – Engine running, used on some Ford system tests.
ERS – Engine RPM Sensor.
ESA – Electronic Spark Advance.
ESC – Electronic Spark Control.
EST – Electronic Spark Timing.
EVP – EGR Valve Position sensor or its circuit.
EVR – EGR Vacuum Regulator or its circuit.
EVRV – Electronic Vacuum Regulator Valve. Controls EGR
vacuum.
EXHAUST GAS OXYGEN SENSOR – Sensor that changes
its voltage output as exhaust gas oxygen content changes as
compared to oxygen content of the atmosphere. The constantly
changing electrical signal is used to control fuel mixture.
EXHAUST GAS RECIRCULATION – Procedure where a
small amount of exhaust gas is readmitted to combustion
chamber to reduce peak combustion temperatures, thus
reducing NOx.
FAIL SAFE – or Fail Soft: any attempt by a computer to
compensate for a fault or lost signal, usually by substituting
fixed replacement valves.
FEEDBACK CARBURETOR (FBC) – System of fuel control
employing a computer controlled solenoid that varies the
carburetors air/fuel mixture.
FEEDBACK CARBURETOR ACTUATOR – Computer
controlled stepper motor used on Ford feedback carburetors,
that varies air/fuel mixture.
FMEM – Failure Mode Effects Management. Sometimes
referred to limp-in mode.
FTO – Filter Tach Output. An output from Ford DIS TFI IV
module which provides a filtered ignition signal to the
processor in order to control dwell.

81 Chapter 6
 Glossary
6 GLOSSARY OF TERMS AND ABBRREVIATIONS

GND, GRD or GRND – Ground. Common line leading to the

negative side of the battery.
HALL EFFECT –Process where current is passed through a
small slice of semiconductor material at the same time as a
magnetic field to produce a small voltage in the semiconductor.
HARD FAULT – Fault present during current engine
operating cycle. Opposite of an intermittent fault which does
not stay present.
HBV – Heater Blower Voltage input to EEC-IV processor
reflecting heater blower voltage demand.
HEDF – High-speed Electro-Drive Fan relay or its circuit.
HEGO – Heated Oxygen Sensor or its circuit.
HIC – Hot Idle Compensator.
H.O. – Height Output
HSC – High Swirl Combustion
IAC – Idle Air Control.
IAS – Inlet Air Solenoid valve or its circuit.
IAT – Intake air temperature sensor, performs same function
as MAT sensor.
ICM – Integrated Control Module.
IDLE TRACKING SWITCH – An input device that sends a
signal to the computer to indicate a closed throttle condition.
IDM – Ignition Diagnostics Monitor. Continuous monitor of
ignition input to EEC-IV processor used to detect intermittent
ignition faults.
IGN – Ignition.
INTERMITTENT FAULT – Fault which occurred during a
previous engine operating cycle. Intermittent fault may have
set a fault code which is still present in PCM memory.
IRCM – Integrated Relay Control Module, used on some Ford
systems.
ISA – Idle Speed Actuator. Extends or retracts to control
engine idle speed and to set throttle stop angle during
deceleration.
ISC – Idle Speed Control, either computer control motor, air
bypass valve, or any device used to control idle rpm.
ITS – Idle Tracking Switch.
KAM – Keep Alive Memory. Battery power memory locations
in computer used to store failure codes and some diagnostic
parameters.

Chapter 6 82
Glossary
GLOSSARY OF TERMS AND ABBRREVIATIONS 6
KAPWR – Keep Alive Power, used to power KAM circuit of
the processor.
KNOCK SENSOR (KS) – Input device that responds to spark
knock, caused by over advanced ignition timing.
KOEO – Key On/Engine Off.
KOER – Key On/Engine Running.
LEAN MIXTURE – Air/fuel mixture that has excessive
oxygen left after all fuel in combustion chamber has burned, 1
part fuel to 15 or more parts air.
LED – Light Emitting Diode.
LOCK UP TORQUE CONVERTER – Converter with
internal mechanism that locks turbine to impeller when
engaged.
LUS – Lock-Up Solenoid.
M/C – Mixture control or mixture control solenoid.
MAF – Mass Air Flow sensor, used to measure amount of
airflow through the throttle body.
MAP – Manifold Absolute Pressure sensor or its circuit.
MAT – Manifold Air Temperature.
MFI – Multi-port Fuel Injection.
MIL – Malfunction Indicator Light. Check engine light.
MICROPROCESSOR CONTROL UNIT (MCU) – The
controlling computer, used on early Ford feedback carburetor
systems and all 5.8L feedback carburetor equipped Fords.
MIXTURE CONTROL SOLENOID – Device installed on
carburetor, that regulates the air/fuel ratio.
MLP – Manual (shift) Lever Position sensor or its circuit.
MPFI – Multi-Port Fuel Injection.
MULTI-PORT FUEL INJECTION – Individual injectors for
each cylinder mounted in intake manifold. Injectors are pulsed
in groups rather than individually.
NDS – Neutral Drive Switch.
NGS – Neutral Gear Switch or its circuit.
NON-VOLATILE MEMORY – Memory retained in block
learn cells (not affected by turning the ignition ON or OFF).
NOx – Nitrous Oxides.
NPS – Neutral Pressure Switch or its circuit.
OCT ADJ – Octane Adjust device which modifies ignition
spark.

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6 GLOSSARY OF TERMS AND ABBRREVIATIONS

OHC – Overhead Cam

OXYGEN SENSOR – Sensor that changes its voltage output
as exhaust gas oxygen content changes as compared to the
oxygen content of the atmosphere. The constantly changing
electrical signal is used to control fuel mixture.
PCM – Powertrain Control Module. Computer that controls
engine fuel, ignition and emission related functions.
PCV – Positive Crankcase Ventilation. System that controls
flow of crankshaft vapors into engine intake manifold where
they are burned in combustion rather then being discharged
into the atmosphere.
PFE – Pressure Feedback EGR sensor or its circuit.
PFI – Port Fuel Injection.
PIP – Profile Ignition Pickup.
PORTED VACUUM SWITCH – Temperature actuated
switch that changes vacuum connections when the coolant
temperature changes.
POT – Potentiometer.
POWERTRAIN CONTROL MODULE – Same as ECM, but
also controls electronically controlled automatic transmission.
PROFILE IGNITION PICKUP – A Hall effect vane switch
that furnishes crankshaft position data to the EEC-IV
processor.
PROM – Programmable Read Only Memory.
PSPS – Power Steering Pressure Switch. Signal is used by
computer to compensate for power steering loads.
PVS – Ported Vacuum Switch.
QUICK TEST – A functional diagnostic test for Ford EEC-IV
system, consisting of test hookup, key on engine off, engine
running and continuous self test models.
RAP – Retained Accessory Power.
RELAY – Switching device operated by a low current circuit,
which controls opening and closing of another higher current
circuit.
RELIEF VALVE – Pressure limiting valve located in exhaust
chamber of thermactor air pump. Relieves part of exhaust
airflow if pressure exceeds a calibrated value.
RICH MIXTURE – Air/fuel mixture that has more fuel than
can burn completely, 1 part fuel to 14 or less parts air.
SAW – Spark Advance Word, and also Spark Angle Word.
SC – Super Charged

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GLOSSARY OF TERMS AND ABBRREVIATIONS 6
SCC – Spark Control Computer.
SEFI – Sequential Electronic Fuel Injection. Injectors located
in intake ports that inject fuel triggered by ignition timing.
SELF-TEST – One of 3 subsets of Ford EEC-IV quick test
modes.
SES – Service Engine Soon light.
SFI – Sequential Fuel Injection,type of MFI with injectors
pulsed individually based on engine firing order.
SHO – Super Height Output
SIG RTN – Signal Return circuit for all sensors except HEGO.
SIL – Shift Indicator Light. Indicates to driver optimum time
to shift gears.
SIR – Supplemental Inflatable Restraint (SIR) system; air
bag.
SIS – Solenoid Idle Stop.
SOLENOID – Wire coil with a movable core which changes
position by means of electromagnetism when current flows
through the coil.
SPARK RETARD SOLENOID – Output device that receives
an output signal from Ford MCU system to bleed distributor’s
vacuum advance when spark knock occurs.
SPOUT – Spark output signal from EEC-IV processor to TFI-
IV module, used to control amount of timing retard.
SSI – Solid State Ignition system.
STI – Self Test Input (Ford) circuit in EEC or MCU systems.
Used to place computer into testing mode.
STO – Self Test Output (Ford) circuit in EEC or MCU
systems. Used by computer to send testing and fault codes to
tester.
T.V. – Throttle Valve.
TAB – Thermactor Air Bypass solenoid.
TACH INPUT – Engine rpm signal sent to computer from
ignition coil primary circuit.
TAD – Thermactor Air Diverter solenoid.
TBI – Throttle Body Injection (Fuel).
TCC – Torque Converter Clutch.
TCP – Temperature Compensating Pump.
TDC – Top Dead Center.
TFI – Thick Film Ignition module. Controls coil and ignition
operation on most Ford vehicles.

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6 GLOSSARY OF TERMS AND ABBRREVIATIONS

THERMACTOR AIR BYPASS SOLENOID – Solenoid

switches engine manifold vacuum. Vacuum reacts on
thermactor bypass valve to bypass thermactor air to the
atmosphere. Used on Ford MCU feedback carburetor system.
THERMACTOR AIR CONTROL VALVE – Combines
function of a normally closed air bypass valve and an air
diverter valve in one integral valve.
THERMACTOR AIR DIVERTER SOLENOID – Solenoid
switches engine manifold vacuum. Vacuum switches
thermactor air from downstream (past EGO sensor) to
upstream (before EGO sensor) when solenoid is energized.
Used on Ford MCU feedback carburetor system.
THERMACTOR AIR SYSTEM – Efficiency of catalytic
converter is dependent upon temperature and chemical
makeup of exhaust gases. These requirements are met by the
thermactor air supply system.
THREE-WAY CATALYST – Combines 2 converters in 1
shell. Controls NOx, HC and CO. Also called dual catalytic
converter.
TIMING – Relationship between spark plug firing and piston
position.
TK – Throttle Kicker solenoid, when energized, supplies
manifold vacuum to throttle kicker actuator as directed by
computer to compensate for engine loads. Also called idle-up
system.
TOT – Transmission Oil Temperature sensor.
TP – Throttle Position sensor or its circuit. Used to signal
computer the position of the throttle plates.
TPI – Tuned Port Injection, a type of MFI with intake tubes
designed to be tuned for performance. Most TPI engines are
also SFI.
TTS – Transmission Temperature Switch.
TVS – Temperature Vacuum Switch.
TVV – Thermal Vent Valve.
TWC – Three-Way Catalyst.
VACUUM – A term to describe a pressure that is less than
atmospheric pressure.
VACUUM ADVANCE – Advances ignition timing with
relation to engine load or computer signals.
VAF – Vane Air-Flow sensor or its circuit.
VAT – Vane Air-Flow Temperature sensor.

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Glossary
GLOSSARY OF TERMS AND ABBRREVIATIONS 6
VM – Vane Meter or air flow meter.
VSS – Vehicle Speed Sensor.
WOT – Wide Open Throttle or Wide Open Throttle switch.
ZONED VACUUM SWITCHES – 3 switches used on Ford
MCU system that provides input signals to MCU, regarding
engine load.

87 Chapter 6
 Glossary
6

Chapter 6 88
Warranty and Service
LIMITED ONE YEAR WARRANTY 7
LIMITED ONE YEAR WARRANTY
The Manufacturer warrants to the original purchaser that this
unit is free of defects in materials and workmanship for a
period of one (1) year from the date of original purchase. If the
unit fails within the one (1) year period, it will be repaired or
replaced, at the Manufacturer's option, at no charge, when
returned prepaid to the Technical Service Center with Proof of
Purchase. The sales receipt may be used for this purpose.
Installation labor is not covered under this warranty.
All replacement parts, whether new or re-manufactured,
assume as their warranty period for only the remaining time
of this warranty. This warranty does not apply to damage
caused by improper use, accident, abuse, or if the product was
altered or repaired by anyone other than the Manufacturer's
Technical Service Center. Consequential and incidental
damages are not recoverable under this warranty. Some states
do not allow the exclusion or limitation of incidental or
consequential damages, so the above limitation or exclusion
may not apply to you.
This warranty gives you specific legal rights, and you may also
have other rights, which vary from state to state. No portion of
this warranty may be copied or duplicated without the
expressed written permission from the Manufacturer.

TECHNICAL ASSISTANCE AND WARRANTY SERVICE

Products requiring service should be returned as follows:
1. Call the Technical Service Center to obtain a Return
Reference Number:
2. Package the product carefully to prevent shipping damage
3. Include your name, return address, and a day contact
phone
4. Enclose a copy of the dated sales receipt
5. Describe the problem
6. Ship prepaid to: Technical Service Center, 17291 Mt.
Herrmann Street, Fountain Valley, CA 92708 U.S.A.
For Technical Assistance/Warranty Service, contact us at:
Phone: USA & Canada 1-800-544-4124, Others
714-241-6805; Fax: 714-432-7910; Web: www.iEquus.com;
Email: service@iEquus.com

89 Chapter 7
 Warranty and Service

Chapter 7 90
Notes
Notes
FORD DIGITAL
CODE READER
(Back Cover)